Leprosy (Hansen Disease)

Meet the patient

A 28-year-old agricultural worker from an endemic district notices he can no longer feel the heat of a cooking pan with his right little finger. On the forearm is a single, sharply demarcated hypopigmented patch with no hair and no sweat; the ulnar nerve at the elbow is a thick, tender cord. He has had the patch for months and ignored it.[2]

The two questions this man forces you to answer are the two that decide every leprosy case: is the patch anaesthetic? (loss of sensation in a hypopigmented lesion, with a thickened nerve, is leprosy until proven otherwise — vitiligo and pityriasis are not anaesthetic) and will he lose nerve function before I treat him? (lepra reactions can wreck a nerve in 24 hours). Hold those two questions and every section below slots into place.[1][2]

One bacillus, one tropism — why skin and nerves

Leprosy is the only human bacterial disease that regularly destroys peripheral nerves. Everything that matters about the disease flows from a single molecular fact: M. leprae has a tropism for Schwann cells of peripheral nerves and dermal macrophages in cooler tissues — skin, peripheral nerves, nasal mucosa, anterior eye and testes, all around 30 to 33 degrees C.[1][3]

M. leprae is obligate intracellular, weakly acid-fast, and slow-growing — a doubling time of about 14 days — and it does not grow on artificial media. The historic research models are the mouse foot-pad (Shepard, 1960) and the nine-banded armadillo (Kirchheimer, 1971). Its surface phenolic glycolipid-1 (PGL-1) binds laminin-2 (merosin) and α-dystroglycan in the basal lamina of Schwann cells, allowing entry by α-dystroglycan-mediated endocytosis; inside the Schwann cell the bacillus is sheltered from immune surveillance and from many antibiotics, replicates slowly, eventually lyses the cell, and spreads to adjacent nerves and dermal macrophages.[1][5]

Etymology for viva gold: Hansen disease honours Gerhard Armauer Hansen, the Norwegian physician who in 1873 became the first person to identify a bacterium as the cause of a human disease — M. leprae — under the microscope, before Koch formalised the germ theory. The older name lepra is from the Greek lepros, "scaly", a description of the skin that long outlived its ignorance of the nerve. The disease's stigma is older than its name; the science is older than the stigma's end.[2]

The spectrum is the immunity — Ridley-Jopling and the WHO rule

The whole clinical skill of leprosy is reading where the patient sits on the immunological spectrum, because that single decision sets the smear result, the infectivity, the treatment duration, and the risk of reactions. The organism is the same; the host's T-cell response decides the disease.[1][3]

The Ridley-Jopling spectrum (1966) runs from the tuberculoid pole (TT) — strong cell-mediated immunity, paucibacillary — through three unstable borderline groups (BT, BB, BL), to the lepromatous pole (LL) — no CMI, multibacillary. The WHO operational classification is the bedside rule that chooses MDT duration: paucibacillary (PB, 1 to 5 lesions) versus multibacillary (MB, more than 5 lesions or smear-positive).[1][2]

[1]

Two further clinical forms deserve recognition. Indeterminate leprosy is the earliest presentation — a faint hypopigmented macule with vague sensory impairment, often in a child — which then polarises to TT or LL or self-resolves. Pure neuritic leprosy (no skin lesion but a thickened tender sensory nerve with mononeuropathy or mononeuritis multiplex) is particularly common in India and frequently missed.[2]

[2]

How common, who, and why India carries the burden

Leprosy is reported from over 100 countries but is heavily concentrated in a handful of high-burden nations. India, Brazil and Indonesia together account for the majority of new cases worldwide, and India alone contributes about 60 percent of the global total of new cases detected annually. The global burden has fallen since MDT was introduced in 1981 to 1982, but new-case detection has plateaued — driven by ongoing transmission, active case-finding that reveals hidden cases, and the long incubation period.[1][4]

[1]

Transmission is via prolonged close contact with an untreated multibacillary case, principally through nasal droplets — M. leprae multiplies in the nasal mucosa and is shed in secretions. The human is the major reservoir; in the Americas the nine-banded armadillo is a zoonotic source (genotype 3I). Skin-to-skin transmission is much less efficient than once thought.[1]

The incubation period is long — typically 2 to 12 years (mean about 5), occasionally longer — which is why disease can appear years after exposure and why contact-tracing spans many years. Only about 5 to 10 percent of exposed individuals develop clinical leprosy, reflecting the dominant role of host immunity and genetic susceptibility (associations with HLA-DR2 and DR3, PARK2 and PACRG, NOD2/CARD15, TLR1 and TIRAP polymorphisms).[1]

Risk factors: household contact with an untreated MB case, poverty and overcrowding, malnutrition, geographic origin (tropical belt), genetic susceptibility, and immunosuppression. A bimodal age distribution is observed, with peaks in young adolescence (10 to 15 years) and adulthood (30 to 60 years); childhood disease reflects ongoing local transmission.[4]

The WHO Global Leprosy Strategy 2021 to 2030 ('Towards zero leprosy') targets (1) interruption of transmission in 120 countries, (2) zero new grade-2 disability (visible deformity) in children, and (3) repeal of all discriminatory laws. India's National Leprosy Eradication Programme (NLEP) implements active case-finding campaigns in endemic districts, SDR-PEP for contacts, Accompanied MDT, Disability Prevention and Medical Rehabilitation (DPMR), and education to combat stigma.[8]

The immune decision — why TT and LL look like different diseases

Position on the Ridley-Jopling spectrum is the host's immune decision, not the organism's. Each pole produces a characteristic histology, smear result and clinical phenotype — and the unstable middle is where reactions strike.[1]

• Tuberculoid pole (TT) — a strong Th1 / cell-mediated response dominated by CD4+ T-helper-1 cells, IL-2, IFN-γ and TNF-α activates macrophages to kill intracellular bacilli and forms well-organised epithelioid granulomas with Langhans giant cells. Few bacilli survive (paucibacillary); the cost is bystander granulomatous destruction of nerves.
• Lepromatous pole (LL) — the Th1 response is switched off in favour of a Th2 / Treg response (IL-4, IL-5, IL-10, TGF-β). Macrophages fail to kill the organism, become foamy "Virchow" cells stuffed with bacilli (globi), and the patient mounts high-titre antibodies (which do not protect). Tissue destruction is paradoxically less, but bacillary load is enormous.
• Split tolerance — the high humoral antibody titres (anti-PGL-1) in LL paradoxically coexist with anergy to M. leprae antigens.

[1] [3]

Nerve injury — why leprosy is the great mimic of mononeuropathy

Leprosy is the only human bacterial disease that regularly damages peripheral nerves, and nerve damage is the central complication — the source of claw hand, foot drop, plantar ulcers and blindness. The mechanisms stack:[5][7]

1. Direct Schwann-cell infection and demyelination — the bacillus multiplies in Schwann cells causing segmental demyelination; in LL, bacilli disseminate along the nerve via the perineurium and endoneurial vessels.
2. Granulomatous inflammation and caseation — in TT or BT, epithelioid granulomas form inside the nerve and caseate, destroying fascicles.
3. Oedema and compression — the perineurium is a rigid sheath; intraneural oedema during reactions raises endoneurial pressure and produces ischaemic fascicular injury. This is why reversal reactions cause acute, compressive, salvageable nerve damage — high-dose steroids within 24 hours can reverse it.
4. Vasa nervorum vasculitis — in BL, LL and ENL, immune-complex vasculitis of epineurial vessels produces infarction.
5. Fibrosis — end-stage, the nerve is replaced by fibrous tissue (irreversible).

[5]

The result is loss of autonomic, sensory and motor fibres in the territory of the involved peripheral nerve — anaesthesia, anhidrosis, and muscle wasting and weakness in the distribution of that nerve, not the dermatomal or stocking-glove pattern of metabolic neuropathy.[5]

The eight nerves to palpate — U-PEST-CRF:[5]

• Ulnar (olecranon groove) → claw hand
• Posterior auricular (mastoid) → facial nerve territory
• Examine the greater auricular (neck) — pure sensory, cosmetic
• Superficial peroneal (fibular neck) → foot drop
• Tibial posterior (behind the medial malleolus) → claw toes, plantar ulcers
• Cutaneous radial (wrist) → sensory loss on the dorsum of the hand
• Radial (spiral groove) → wrist drop
• Facial (stylomastoid foramen to face) → lagophthalmos

[5] [5] [7]

Lepra reactions — the emergencies that decide disability

Reactions are acute immunological flares superimposed on chronic disease. They are the most important cause of new nerve damage and must be recognised and treated within hours, not days. Every new weakness or nerve pain in known leprosy is a reaction until proven otherwise.[1][6]

[1] [6]

• Type 1 (reversal) reaction — a delayed (type IV) hypersensitivity reaction to M. leprae antigens, occurring in borderline (BT, BB, BL) patients, often within months of starting MDT, in pregnancy, or with intercurrent infection. Existing skin lesions become erythematous, oedematous and tender, and there is acute neuritis — a painful, tender, thickened nerve with new motor loss. There is no systemic inflammation and no fever. Treatment: corticosteroids.
• Type 2 reaction (erythema nodosum leprosum, ENL) — an immune-complex (type III) reaction in BL or LL patients, characterised by deposition of immune complexes in vessels with neutrophilic vasculitis and a TNF-α-driven systemic inflammatory response. Patients develop crops of tender erythematous nodules on the face and extensor limbs, with fever, malaise, arthralgia, iritis, dactylitis, orchitis, glomerulonephritis and neuritis. Episodes can be recurrent over years. Treatment: thalidomide, clofazimine, corticosteroids.

[1] [6]

The three cardinal signs and the spectrum of presentation

The three cardinal signs of leprosy (WHO) are the diagnostic core: (1) hypopigmented or erythematous skin lesion or lesions with definite sensory loss, (2) thickened peripheral nerves with sensory and/or motor deficit in the distribution of the affected nerve, (3) positive skin smear. Diagnosis can be made on the first two cardinal signs alone, because most PB cases are smear-negative.[1]

Tuberculoid (TT) leprosy. A single (or up to three) sharply demarcated hypopigmented or erythematous patch anywhere on the body, with loss of sensation (cotton wool, pinprick, temperature), loss of hair (alopecia) and loss of sweating (anhidrosis). A nearby peripheral nerve is often palpably thickened and tender (the ulnar, radial cutaneous, or posterior auricular). Skin smear is negative.[2]

Borderline (BT, BB, BL) leprosy. Lesions are more numerous, asymmetric and polymorphic — macules, plaques, annular lesions with a punched-out centre. BT lesions resemble TT but are more numerous; BL lesions approach the lepromatous pattern but retain some asymmetry. Borderline patients are the most likely to develop type 1 reactions, because their CMI is unstable.[1]

Lepromatous (LL) leprosy. Numerous, symmetric, ill-defined lesions — macules, plaques, papules and nodules (erythema nodosum-like, but chronic). There is diffuse cutaneous infiltration; the face becomes thickened and corrugated — leonine facies — with eyebrow alopecia (madarosis), saddle-nose deformity (from nasal cartilage destruction), ear-lobe infiltration, and gynaecomastia (from testicular atrophy). The skin smear is strongly positive.[2]

Neurologically, LL produces symmetric, distal glove-and-stocking sensory loss (from dermal and intraneural infiltration of many small cutaneous nerves) with preservation of tendon reflexes early on; motor loss is late. The nasal mucosa is heavily involved (chronic congestion, epistaxis, septal perforation). The eye is involved via corneal anaesthesia (trigeminal) and lagophthalmos (facial nerve), leading to exposure keratitis; iridocyclitis is direct ocular infection. The testes are infiltrated, producing orchitis, atrophy, infertility and gynaecomastia.[1]

WHO disability grading (reproduced verbatim):[1]

• Grade 0 — no anaesthesia, no visible deformity.
• Grade 1 — anaesthesia present, but no visible deformity or damage.
• Grade 2 — visible deformity or damage of the hands, feet or eyes (claw hand, foot drop, plantar ulcer, lagophthalmos, corneal opacity, visual impairment).[1]

The eye-hand-foot (EHF) score (sum of WHO grades for the two eyes, two hands and two feet, range 0 to 12) monitors disability over time and flags patients at high risk of new nerve damage.[7]

The mimics — sensation in the lesion is the discriminator

A hypopigmented or nodular skin lesion is not always leprosy. The decisive discriminator is sensation in the lesion and the presence of a thickened peripheral nerve — vitiligo, pityriasis and the post-inflammatory patches are not anaesthetic.[2]

[2] [2]

For peripheral neuropathy with thickened nerves, the leprosy-distinctive feature is the combination of cutaneous anaesthesia and a thickened, tender nerve — which diabetic mononeuropathy, vasculitic mononeuritis multiplex, hereditary neuropathy with pressure palsies (HNPP), and B12 neuropathy do not produce. Charcot-Marie-Tooth disease can produce palpable nerves but is symmetric, slowly progressive and lifelong with a family history.[7]

The bedside round — test sensation, palpate nerves, grade disability

A focused bedside examination is the diagnostic core of leprosy — the slit-skin smear only confirms what the bedside already shows in most PB cases.[1]

Skin examination — inspect the whole skin under good light; identify hypopigmented, erythematous, infiltrative or nodular lesions. For each lesion, test sensation:[5]

• Light touch with a wisp of cotton wool or a Semmes-Weinstein nylon monofilament (10 g) — ask the patient to close the eyes and point to where they feel the touch (compare lesion with normal contralateral skin).
• Temperature with two test-tubes (warm and cold).
• Pain with a sterile pin (compare with normal skin).
• A lesion with definite sensory loss plus a thickened nerve is leprosy.[5]

Nerve palpation — systematically palpate and assess the eight peripheral nerves (see U-PEST-CRF): ulnar at the olecranon groove, radial cutaneous at the wrist, median at the wrist, common peroneal at the fibular neck, posterior tibial behind the medial malleolus, facial branches, posterior auricular over the mastoid, and greater auricular across the sternocleidomastoid. Assess each for thickening, tenderness, consistency (soft, firm, hard), and the presence of an associated motor or sensory deficit.[5]

Voluntary muscle testing (VMT) — test the muscles supplied by each at-risk nerve (first dorsal interosseous for ulnar; abductor pollicis brevis for median; ankle dorsiflexion for common peroneal; orbicularis oculi closure for facial).[5]

The classic trap: every hypopigmented patch is anaesthetic until proven otherwise. The recurring trainee error is to label TT as vitiligo or pityriasis versicolor because the patch is pale — and to omit the sensory test that would have made the diagnosis in ten seconds.[1]

The tests — clinical, then slit-skin smear, biopsy and PCR

The diagnosis is clinical, supported by laboratory tests when the cardinal signs are equivocal or when classification is unclear.[1][3]

Slit-skin smear is the cornerstone laboratory test for multibacillary leprosy. A small (5 mm) incision is made in pinched skin (typically ear lobes and 3 to 4 active lesions); the dermis is scraped with the blade edge, the scrapings smeared, fixed and stained with Ziehl-Neelsen or Fite-Faraco for acid-fast bacilli. The Bacterial Index (BI) is the mean log-10 bacillary load across sites, graded 0 to 6+ on the Ridley logarithmic scale:[1]

• 0 — no bacilli in 100 oil-immersion fields.
• 1+ — 1 to 10 bacilli per 100 fields.
• 2+ — 1 to 10 per 10 fields.
• 3+ — 1 to 10 per field (average).
• 4+ — 10 to 100 per field.
• 5+ — 100 to 1000 per field.
• 6+ — more than 1000 per field (globi or clumps).[1]

The Morphological Index (MI) is the percentage of uniformly stained, viable-appearing bacilli versus granular, dead forms; it falls rapidly after starting rifampicin, a useful early marker of treatment response. PB leprosy is smear-negative; MB leprosy is smear-positive.[1]

Skin biopsy — a wedge biopsy (including subcutaneous fat) taken from the active border of a lesion. Histopathology distinguishes the spectrum:[2][3]

• TT — well-formed epithelioid cell granulomas with Langhans giant cells in the dermis, often around nerves and skin appendages; caseation can occur; bacilli are scarce or absent; a subepidermal free zone is preserved.
• BT — epithelioid granulomas less well-formed, some bacilli may be found in nerves.
• BB — diffuse epithelioid infiltrate with scattered lymphocytes and macrophages; few bacilli.
• BL — macrophage predominance with some epithelioid foci; moderate bacillary load.
• LL — sheets of foamy "Virchow" macrophages filled with bacilli (often in clumps called globi); a characteristic subepidermal free (Grenz) zone separates the infiltrate from the epidermis; numerous plasma cells and lymphocytes.[2][3]

Acid-fast staining of tissue requires the Fite-Faraco method (not plain Ziehl-Neelsen) because M. leprae's cell wall is more readily decolourised by acid than M. tuberculosis.[3]

Nerve biopsy — a sensory cutaneous nerve (the sural, superficial radial, or posterior auricular) is biopsied when pure neuritic leprosy is suspected or the skin biopsy is non-diagnostic. Findings range from epithelioid granuloma (TT) to heavy bacillary infiltration (LL). Nerve biopsy can cause a small permanent sensory deficit at the biopsy site and is reserved for diagnosis-specific indications.[1]

Molecular diagnosis — PCR — M. leprae DNA (target RLEP, 16S rRNA or groEL) detected by PCR in skin smears, biopsies and nerve tissue. PCR is highly sensitive in MB but low sensitivity in PB (few organisms); useful for confirmation and species identification (distinguishing M. leprae from M. lepromatosis).[3]

Serology — anti-PGL-1 antibodies — high sensitivity in LL and BL but low sensitivity in TT and BT; useful for epidemiological surveys and as an adjunct for classification, not for individual diagnosis.[1]

Why culture is impossible — M. leprae does not grow on Lowenstein-Jensen or other artificial media; the historic research model is the mouse foot-pad (Shepard, 1960) and the nine-banded armadillo (Kirchheimer, 1971). The Mantoux test with tuberculin does not diagnose leprosy; it reflects TB exposure or BCG, not leprosy.[3]

Baseline investigations at diagnosis — full blood count (dapsone can cause haemolysis or agranulocytosis), G6PD assay (especially in regions of high prevalence — dapsone is relatively contraindicated in severe deficiency), renal and liver function (rifampicin and dapsone hepatotoxicity), HIV and hepatitis B and C screen (co-infection affects management), urinalysis, BMI (malnutrition is a risk factor), and a chest X-ray if TB co-infection is suspected.[3]

The three time-critical situations — reactions and Lucio

Leprosy itself is rarely a resuscitation emergency, but three situations are time-critical, and each can leave the patient with permanent disability in a day.[1][6]

1. Acute type 1 (reversal) reaction with nerve function impairment — the single most important preventable cause of disability. A patient (typically borderline) presents with inflamed, erythematous, oedematous skin lesions and acute painful neuritis with new sensory or motor loss. Start oral prednisolone 40 to 60 mg once daily (or equivalent) within 24 hours of onset, continue MDT, refer to a specialised leprosy centre, immobilise the affected limb, and monitor with VMT and sensory testing daily. Steroids can save nerve function.[1]

2. Severe type 2 (ENL) reaction — the patient (BL or LL) has crops of painful erythematous nodules, fever and malaise, and may have iritis, orchitis, dactylitis, nephritis, hepatosplenomegaly or neuritis. Management: thalidomide (where licensed and NOT in a woman of childbearing potential without strict contraception) 100 to 300 mg per day, high-dose clofazimine (300 mg per day, reducing over months), NSAIDs and analgesia, antipyretics; short-course corticosteroids for severe systemic involvement; supportive care. Admit if systemic involvement is severe.[6]

3. Lucio phenomenon — a medical emergency with high mortality: painful, irregular, angulated skin ulcers and infarcts on a background of untreated diffuse LL. Management: urgent specialist referral, systemic corticosteroids, MDT, wound care, and treatment of secondary infection.[1]

Acute complications needing immediate intervention: lagophthalmos (eye lubrication plus a night-time eye shield; tarsorrhaphy if persistent), foot drop (ankle-foot orthosis to prevent falls and equinus contracture), claw hand (intrinsic-plus splint, daily passive extension), and plantar trophic ulcer (off-loading, debridement, protective footwear, treatment of secondary infection).[7]

WHO multidrug therapy (MDT) — the curative backbone

MDT is the single most important intervention in leprosy. It is curative, free (donated by Novartis via WHO), blister-packed and well tolerated, and it uses three drugs with different mechanisms to prevent resistance.[1][2]

[1]

Paucibacillary (PB) MDT — 6 months:[1]

• Rifampicin 600 mg orally once monthly (supervised) — powerful bactericidal: a single 600 mg dose kills 99.9 percent of viable bacilli within days; the patient becomes essentially non-infectious after the first dose.
• Dapsone 100 mg orally once daily (self-administered) — bacteriostatic, cheap, oral.
• Duration: 6 months (blister pack of 4 weekly doses).[1]

Multibacillary (MB) MDT — 12 months:[1]

• Rifampicin 600 mg once monthly supervised — bactericidal.
• Clofazimine 300 mg once monthly supervised PLUS 50 mg once daily (self-administered) — weakly bactericidal plus anti-inflammatory (useful in ENL); reservoir effect.
• Dapsone 100 mg once daily (self-administered).
• Duration: 12 months (the historical regimen was 24 months; shortened to 12 in 1998).[1]

Rationale and pharmacology of each drug:[1]

• Rifampicin (600 mg monthly) — inhibits DNA-dependent RNA polymerase; bactericidal; a single dose renders the patient non-infectious; given once monthly because of its long post-antibiotic effect on M. leprae. Side-effects: orange-red discoloration of urine, tears and sweat (counsel), hepatotoxicity (monitor LFTs), thrombocytopenia, a flu-like syndrome, gastrointestinal upset; potent inducer of hepatic enzymes — reduces the efficacy of oral contraceptives (counsel to use a barrier too), warfarin and protease inhibitors.
• Dapsone (100 mg daily) — folate antagonist (inhibits dihydropteroate synthase), bacteriostatic, cheap, oral. Side-effects: dose-related haemolysis (especially in G6PD deficiency — check before starting), methaemoglobinaemia, agranulocytosis (rare but serious), dapsone hypersensitivity syndrome (fever, rash, lymphadenopathy, hepatitis, eosinophilia — resembles DRESS, in the first 6 weeks), hepatitis, peripheral neuropathy (rare).
• Clofazimine (300 mg monthly plus 50 mg daily) — binds mycobacterial DNA; weakly bactericidal; anti-inflammatory; long tissue half-life (reservoir). Side-effects: reddish-brown skin pigmentation (counsel; resolves months after stopping), ichthyosis and dry skin, GI upset, and crystal deposition in mesenteric nodes. The pigmentation can worsen stigma; counsel patients at the start.[1]

Special regimens:[1]

• Single-dose rifampicin post-exposure prophylaxis (SDR-PEP) — a single dose of rifampicin given to contacts of an index case reduces the risk of leprosy by about 50 to 60 percent in the first 2 years; now endorsed by the WHO 2018 guideline. Conaindicated in pregnancy, in confirmed leprosy, and in contacts of PB single-lesion cases (low yield).
• Uniform MDT (U-MDT) — a 6-month 3-drug regimen for both PB and MB — is being studied; not yet standard of care.
• Monotherapy is forbidden — it selects for resistance. Historically, dapsone monotherapy (1960s to 80s) produced dapsone-resistant relapse; rifampicin monotherapy rapidly selects rifampicin-resistant M. leprae. Always use combination MDT.[1]

Managing reactions and established disability

Type 1 (reversal) reaction:[1][5]

• Corticosteroids — oral prednisolone 40 to 60 mg per day (maximum 1 mg/kg/day), maintained for 2 to 4 weeks, then tapered over 12 to 24 weeks (avoid a rapid taper — recurrence risk). Severe neuritis may need IV methylprednisolone.
• Continue MDT throughout the reaction.
• Rest the affected limb; immobilise if acute neuritis; treat precipitating causes (infection, pregnancy, anaemia).
• Surgical decompression of acutely swollen nerves is reserved for refractory cases and is controversial.[1][5]

Type 2 reaction (ENL):[6]

• Thalidomide — 100 to 300 mg orally at night, reducing to maintenance; the most effective agent for ENL. Strict contraindications: pregnancy (severe teratogen — phocomelia) and women of childbearing potential not on rigorous contraception (use a pregnancy prevention programme). Monitor for peripheral neuropathy, somnolence, thrombosis.
• Clofazimine — 300 mg per day for several weeks, reducing to 100 mg per day; anti-inflammatory; useful for recurrent ENL.
• Corticosteroids — prednisolone for severe systemic involvement or neuritis; avoid prolonged courses.
• Alternatives or adjuncts — pentoxifylline, colchicine, ciclosporin, methotrexate, TNF inhibitors for refractory cases.
• Continue MDT.[6]

The goal of disability prevention and medical rehabilitation (DPMR) is to preserve nerve function and limit secondary damage:[7]

• Anaesthetic hands and feet — patient self-care education: daily inspection for cuts and blisters, soaking and oiling skin, protective footwear (microcellular rubber, MCR) for plantar anaesthesia, avoiding burns and trauma.
• Claw hand — intrinsic-plus splint, daily passive interphalangeal extension, hand therapy; reconstructive surgery (tendon transfer, e.g. extensor carpi radialis longus to lateral band) once disease is stable for at least 6 months.
• Foot drop — ankle-foot orthosis (AFO) to prevent falls and equinus contracture; tendon transfer (tibialis posterior to lateral cuneiform) once stable.
• Lagophthalmos — night-time eye shield and lubricants during the day; tarsorrhaphy or gold-weight upper-lid implant for permanent lagophthalmos.
• Plantar ulcer — off-loading (rest, crutches, total-contact cast), debridement, treatment of secondary infection, and after healing, MCR footwear.[7]

The subtypes and scenarios that change the plan

Borderline disease and type 1 reactions — borderline patients (BT, BB, BL) carry unstable CMI: a sudden upswing in Th1 immunity (triggered by MDT killing bacilli and releasing antigen, or by pregnancy, anaemia, intercurrent infection) upgrades the patient toward the tuberculoid pole — clinically, a type 1 (reversal) reaction. New lesions may appear; existing lesions become inflamed and oedematous; acute neuritis is the feared complication. Treatment: corticosteroids as above. Reactions may recur and need a prolonged steroid taper.[1][5]

Lepromatous disease and type 2 reactions (ENL) — in LL or BL, the high bacillary load and antigenaemia precipitate immune-complex vasculitis, ENL. Patients are systemically unwell, with crops of painful nodules, fever, iritis, orchitis, nephritis and neuritis. ENL is recurrent and a major cause of morbidity; thalidomide is the most effective agent. Long-term amyloidosis (AA type) can complicate recurrent ENL, presenting as nephrotic syndrome or renal failure.[6]

Lucio phenomenon — a severe necrotising vasculitis of small dermal vessels seen in diffuse LL (Lucio-Latapí), endemic to Mexico and Central America. Painful, angulated, irregular skin ulcers and infarcts appear abruptly; systemic toxicity is marked; mortality is high. Management: systemic corticosteroids, MDT, wound care, infection control, supportive care.[1]

Pure neuritic leprosy — no skin lesion but a thickened, tender peripheral nerve with sensory or motor loss in its distribution — a common presentation in India. Diagnosis: nerve biopsy (or PCR), exclusion of other mononeuropathies. Treated as PB or MB based on smear and clinical judgement.[2]

Indeterminate leprosy — an early faint hypopigmented macule with vague sensory impairment in a child (often a household contact). Most resolve spontaneously; those that progress require MDT.[1]

The complications — nerve damage is the central one

The deformities of untreated leprosy — claw hand, foot drop, lagophthalmos, plantar ulcers, autoamputation, blindness — result from peripheral nerve damage. They are largely irreversible once established, which is why early diagnosis and prompt treatment of reactions is the single most important prevention.[7]

[7]

Classic pitfalls (each costs a nerve):[1][5]

• Missing leprosy because sensation was not tested in a hypopigmented patch — every patch is anaesthetic until proven otherwise.
• Mislabelling TT as vitiligo or pityriasis versicolor because the patch is hypopigmented — vitiligo and pityriasis are not anaesthetic.
• Failing to recognise a type 1 reaction as the cause of acute nerve damage in a borderline patient — every new weakness in known leprosy is a reversal reaction until proven otherwise; start steroids within 24 hours.
• Stopping MDT prematurely — relapse risk; MDT must be completed (PB 6 months, MB 12 months) even if lesions look "cured".
• Prescribing thalidomide to a pregnant woman (or one of child-bearing potential without rigorous contraception).
• Forgetting that dapsone causes haemolysis in G6PD deficiency — screen where feasible.
• Forgetting that rifampicin reduces OCP and warfarin efficacy — counsel and adjust.[1][5]

Prognosis, disposition and surveillance

Leprosy is curable with WHO MDT, with a bacteriological cure rate near 100 percent and a relapse rate under 1 percent per year after completion. Patients become non-infectious after the first dose of rifampicin; isolation is never required. The prognosis for nerve function depends on how early treatment is started and how promptly reactions are treated — established nerve damage before treatment is largely irreversible. Patients with grade-2 disability at diagnosis have a worse functional outcome and need long-term DPMR.[1][7]

Surveillance after MDT — clinical and sensory examination (and serial slit-skin smears for MB) for 2 to 5 years to detect relapse (most relapses occur in the first 3 years) and new reactions. Relapse is treated with the same WHO MDT regimen (resistance is rare if MDT was used).[1]

Discharge criteria — completed MDT course, no active reaction, all reversible nerve function impairment treated, grade-2 disability managed with appropriate footwear, splint or eye care, and the patient educated in self-care. Patients should be advised to return promptly if they develop new skin lesions, nerve pain, weakness or new disability.[8]

Special populations — pregnancy, lactation, children, HIV, G6PD

Pregnancy — leprosy may worsen during pregnancy and the postpartum (the immune shift toward Th2 in pregnancy drives disease activity; the Th1 rebound postpartum triggers type 1 reactions). MDT (PB and MB) is safe in pregnancy — continue throughout. Thalidomide is absolutely contraindicated (teratogen). Rifampicin reduces OCP efficacy — counsel. Clofazimine crosses the placenta and is excreted in breast milk; it is compatible with breastfeeding but infants should be monitored for skin pigmentation and GI upset.[4]

Lactation — MDT is compatible with breastfeeding. Clofazimine is excreted in milk and may lightly pigment the infant's skin (cosmetic, reversible).[1]

Children — a significant fraction of new cases in endemic areas; grade-2 disability in a child is a public-health failure indicating ongoing transmission. Weight-based dosing in WHO blister packs:[1]

• 10 to 14 years — adult-dose MDT (PB and MB).
• Under 10 years — half the adult dose.
• Under 5 years or under 15 kg — about a quarter of the adult dose.[1]

HIV co-infection — HIV does not appear to alter the natural history of leprosy in patients on antiretroviral therapy (ART), but immune reconstitution inflammatory syndrome (IRIS) after starting ART can unmask leprosy or trigger type 1 reactions. Co-management with HIV services is essential.[4]

G6PD deficiency — dapsone causes dose-related haemolysis and methaemoglobinaemia, particularly in G6PD-deficient patients. Screen where feasible; if deficient, use a MB regimen without dapsone (rifampicin plus clofazimine plus a fluoroquinolone such as ofloxacin, or minocycline) under specialist guidance.[3]

Evidence, guidelines and regional differences

WHO Guidelines for the Diagnosis, Treatment and Prevention of Leprosy (2018) formalised the current standard of care:[4]

• 3-drug MDT for all MB (rifampicin plus clofazimine plus dapsone, 12 months) and 2-drug MDT for all PB (rifampicin plus dapsone, 6 months) — replacing the previous recommendation of 3-drug MB only for smear-positive cases, simplifying operational delivery.
• Single-dose rifampicin post-exposure prophylaxis (SDR-PEP) for contacts of an index case.
• Accompanied MDT — the patient may take home the full course to encourage completion; supervised monthly rifampicin where possible.
• No isolation; no routine separation of patients from family or community.[4]

WHO Global Leprosy Strategy 2021 to 2030 — 'Towards zero leprosy' targets: (1) 120 countries achieve interruption of transmission (no new autochthonous cases in children under 5); (2) zero new grade-2 disability in children; (3) repeal of all discriminatory legislation (e.g. India's repeal of the colonial-era Leprosy Act).[8]

India — National Leprosy Eradication Programme (NLEP) delivers WHO MDT free through primary health centres, runs Leprosy Case Detection Campaigns (LCDC) in endemic districts, provides SDR-PEP to contacts, supports Disability Prevention and Medical Rehabilitation (DPMR) with reconstructive surgery camps, and operates a stigma-reduction public-awareness campaign. Accompanied MDT and ASHA-based referral are operational innovations.[8]

[4]

Controversies and research gaps — the MB MDT duration (12 months is now standard; an older 24-month regimen and a proposed 6-month uniform MDT (U-MDT) remain under study); chemoprophylaxis versus vaccination (BCG gives partial protection, about 50 percent, and is more effective against PB than LL; SDR-PEP gives additive benefit; a specific leprosy vaccine is not yet available); early case-finding tools (anti-PGL-1 serology, contact tracing, PCR on nasal swabs); the treatment of lepra reactions (thalidomide is teratogenic and neuropathic; alternative anti-TNF agents and lenalidomide are being explored for ENL); and M. lepromatosis, a second species causing diffuse leprosy and Lucio phenomenon, which is increasingly recognised.[4]

The mantra, and the mnemonic

[1]

The mantra: anaesthetic patch plus thickened nerve is leprosy; six months for PB, twelve for MB; steroids for reversal, thalidomide for ENL — and never miss a reaction, because the nerve you spare is the hand you save.[1][6]

Ward-round test — three stems, thirty seconds each

Stem 1 — the man from the top of the topic (answer)

The 28-year-old farmer with a single hypopigmented, hairless, anaesthetic forearm patch and a thickened tender ulnar nerve. What is this, and what is the first step? Model: This is tuberculoid (paucibacillary) leprosy — the cardinal sign of an anaesthetic patch with a thickened nerve makes the diagnosis; vitiligo and pityriasis are not anaesthetic. Confirm with a slit-skin smear (likely negative in PB) and a skin biopsy from the active border (epithelioid granulomas, few or no bacilli, Fite-Faraco stain). Start WHO PB-MDT — rifampicin 600 mg once monthly supervised plus dapsone 100 mg daily for 6 months; check G6PD and LFTs first. Counsel the patient that he becomes non-infectious after the first rifampicin dose and that no isolation is needed. Watch for a type 1 (reversal) reaction in the first months.[1]

Stem 2 — the borderline patient with new weakness (answer)

A borderline leprosy patient two months into MB-MDT phones to say his ulnar nerve hurts and he cannot spread his fingers. What happened, and what do you do? Model: This is a type 1 (reversal) reaction with acute neuritis — the commonest cause of new nerve damage in borderline leprosy, triggered by MDT killing bacilli and releasing antigen. Start oral prednisolone 40 to 60 mg once daily within 24 hours, continue MDT, immobilise the limb, and monitor with voluntary muscle testing and sensory testing daily. Steroids can save the nerve; without them, the claw hand may be permanent. Reactions may recur and need a 12 to 24-week taper. Every new weakness in known leprosy is a reversal reaction until proven otherwise.[1][5]

Stem 3 — the LL patient with crops of painful nodules and fever (answer)

A young man with untreated lepromatous leprosy presents with crops of tender red nodules on his face and shins, fever, malaise and a swollen painful testis. What is this, and what is the first-line treatment — and what must you exclude before prescribing it? Model: This is erythema nodosum leprosum (ENL) — a type 2, immune-complex (type III) reaction of BL or LL leprosy. First-line treatment is thalidomide 100 to 300 mg at night, with clofazimine 300 mg daily and short-course corticosteroids for severe systemic involvement; continue MDT. Before prescribing thalidomide you must exclude pregnancy and ensure rigorous contraception in any woman of childbearing potential — thalidomide is a severe teratogen (phocomelia). In a pregnant woman with ENL, use clofazimine and corticosteroids instead. Watch for recurrent ENL, long-term AA amyloidosis, and thalidomide neuropathy.[6]

References

1. [1]Grijsen ML, Nguyen TH, Pinheiro RO, et al. Leprosy. Nature Reviews Disease Primers, 2024.PMID 39609422
2. [2]White C, Franco-Paredes C. Leprosy in the 21st century. Clinical Microbiology Reviews, 2015.PMID 25567223
3. [3]Mungroo MR, Khan NA, Siddiqui R. Mycobacterium leprae: Pathogenesis, diagnosis, and treatment options. Microbial Pathogenesis, 2020.PMID 32931893
4. [4]Rodrigues LC, Lockwood DNj. Leprosy now: epidemiology, progress, challenges, and research gaps. Lancet Infectious Diseases, 2011.PMID 21616456
5. [5]Scollard DM. Mechanisms of nerve injury in leprosy. Clinics in Dermatology, 2015.PMID 25432810
6. [6]Kahawita IP, Lockwood DNj. Towards understanding the pathology of erythema nodosum leprosum. Transactions of the Royal Society of Tropical Medicine and Hygiene, 2008.PMID 18313706
7. [7]Ebenezer GJ, et al. Treatment and Evaluation Advances in Leprosy Neuropathy. Neurotherapeutics, 2021.PMID 34799845
8. [8]Lockwood DNj. Leprosy: too complex a disease for a simple elimination paradigm. Bulletin of the World Health Organization, 2005.PMID 15798849