Bullous pemphigoid

Meet the patient

A 78-year-old man has spent three months itching. His GP treated him for scabies, then eczema, then a "drug reaction", with no benefit. This week he woke to find tense, water-balloon blisters on his trunk, inner thighs and forearms, sitting on red, urticarial skin. He scratches until they bleed.^[1][2]

That prodrome — weeks to months of intractable itch mislabelled as eczema or scabies, then blistering — is the classic BP story, and it is why every elderly patient with unexplained pruritus or an eosinophilic urticarial eruption earns a biopsy. Two questions run the case: is this pemphigoid or pemphigus? (the tense bullae, negative Nikolsky and subepidermal split answer it) and can I control it without sterilising this frail patient with steroids? (the topical-first paradigm answers it).^[1][3]

The clinical signature — tense bullae, negative Nikolsky, the elderly

BP is the commonest autoimmune blistering disease, peak onset 60 to 80 years. The pathognomonic sign is tense bullae (over 1 cm, with a thick roof) on an erythematous or urticarial base, on the trunk, proximal limbs, flexures and lower abdomen; palms and soles are usually spared. The roof is thick because the split is below the epidermis, so the blisters do not rupture as easily as pemphigus.^[1][3]

The Nikolsky sign is negative. Lateral pressure does not detach the epidermis — the single bedside feature that separates BP from pemphigus vulgaris, where it is positive. Mucosal involvement occurs in only 10 to 30 percent and is usually mild and oral, again unlike pemphigus.^[2][3]

^[1]

The pemphigoid family — one mechanism, many faces

BP is the prototype; the pemphigoid subtypes share hemidesmosomal autoimmunity but differ in site, antibody and behaviour. The subtype matters because it sets aggressiveness — mucous membrane pemphigoid scars and blinds, pemphigoid gestationis threatens the fetus, drug-induced pemphigoid can vanish with drug withdrawal.^[1][9]

^{[1] [4] [9] [12]}

Mucous membrane pemphigoid (MMP / cicatricial pemphigoid) is the aggressive cousin: a heterogeneous subset dominated by anti-BP180 (C-terminal), anti-laminin 332 (anti-epiligrin — paraneoplastic association), and anti-integrin α6β4. It is mucosal-dominant — oral, conjunctival, genital, laryngeal, oesophageal — and scars: symblepharon and eventual blindness if untreated. Ocular involvement is an emergency, and it is the key reason MMP is treated more aggressively than cutaneous BP.^[4][12]

Pemphigoid gestationis (PG, "herpes gestationis") is pregnancy-specific BP: onset in the 2nd-3rd trimester or postpartum, periumbilical urticarial plaques progressing to bullae, anti-BP180 NC16A. It recurs in subsequent pregnancies, often earlier and more severe, and carries fetal risk (preterm delivery, small-for-gestational-age) — so obstetric co-management with serial growth scans is mandatory.^[10][11]

Why it blisters — the pathogenesis

The autoantibodies target two hemidesmosomal antigens. Predominantly IgG4 and IgG1 against BP180 (collagen XVII), especially the NC16A extracellular domain — the immunodominant epitope — and BP230 (BPAG1), an intracellular plakin. IgE autoantibodies against BP180 are also important and drive the pruritus.^[1][3]

Antibody binding activates complement (C3), recruits eosinophils, mast cells and neutrophils, and releases proteases (MMP-9, elastase) that cleave BP180 and damage the hemidesmosome-anchoring filament complex. Separation occurs at the lamina lucida, producing the subepidermal blister.^[1]

The response is Th2-driven — IL-4, IL-5, IL-13, IL-31 and high total IgE — which explains the eosinophilia, the pruritus, and the emerging role of dupilumab (anti-IL-4Rα). It also explains why a high IgE predicts omalizumab responsiveness, and why a high eosinophil count flags dupilumab candidacy.^[5]

The disease-activity biomarker is anti-BP180 NC16A ELISA. Circulating titres correlate with blister count, disease activity and relapse risk — rising titres predict flare even before clinical relapse. Anti-BP230 antibodies are positive in 50 to 70 percent and track pruritus and eosinophilia; anti-BP180 NC16A is the single most useful biomarker for monitoring response and guiding taper.^[1]

The neurological link and the drug triggers

BP travels with neurological disease. Cohort studies show a higher prevalence of pre-existing or new-onset Parkinson's disease (around threefold), Alzheimer's dementia, vascular dementia, stroke, epilepsy and multiple sclerosis than in age-matched controls — often preceding the BP by years, suggesting a shared autoimmune mechanism against BP180 isoforms expressed in the nervous system.^[6][8]

A drug trigger is identifiable in roughly 15 to 25 percent of new BP. The mnemonic is GLIP-PS:^[6][7]

^[7]

The classic trap: always take a drug history in any new-onset BP. Checkpoint-inhibitor BP can develop within days to weeks of the first infusion and tends to be severe and refractory, while gliptin and loop-diuretic BP has a median latency of 6 to 12 months that easily obscures attribution. Withdraw the offending drug — it often resolves within weeks to months.^[7]

The differential — three face-offs

Tense versus flaccid, linear versus intercellular, IgG versus IgA, roof versus floor. Four questions at the bedside classify over 90 percent of bullous dermatoses.^[1][9]

^[1]

The third and subtlest face-off is BP versus epidermolysis bullosa acquisita (EBA) — same linear IgG at the BMZ on DIF, so DIF alone cannot tell them apart. The discriminator is the salt-split skin test.^[1]

^{[1] [1]}

The wider differential holds the rest: linear IgA disease ("string of pearls", linear IgA at BMZ), bullous drug eruption (drug history, DIF negative), bullous impetigo (children, positive culture, superficial), bullous lupus (SLE, sun-exposed, granular BMZ), and pseudoporphyria (NSAID or dialysis, dorsal hands, no antibodies).^[1]

Diagnosis — three integrated tests, never one alone

Never rely on serology alone or histology alone. Serology is falsely positive in the elderly with background autoreactivity; histology cannot separate BP from EBA or DH. Three integrated tests make the diagnosis.^[1][4]

1. Histology (lesional punch, 4 mm, from a fresh intact bulla under 24 h old) shows a subepidermal blister with an eosinophil-rich infiltrate in the dermis and blister cavity. Eosinophilic spongiosis — eosinophils tracking into the lower epidermis — is characteristic of the non-bullous prodrome and may be the only H&E finding in papular disease.^[1]

2. Direct immunofluorescence (DIF) of perilesional skin — within 1 to 2 cm of an active lesion, not a bulla roof or floor (they consume immune deposits and give false negatives) — shows linear IgG4 (with C3 in 70 to 80 percent) along the BMZ. This is the gold standard. The contrast with pemphigus is the teaching point that earns marks: pemphigus shows intercellular, chicken-wire IgG4.^[1]

3. Serology confirms and quantifies. IIF on 1 mol/L NaCl salt-split skin — BP antibodies bind the epidermal (roof) side (the BED rule); EBA binds the dermal (floor) side. Anti-BP180 NC16A ELISA is about 85 to 90 percent sensitive and 95 percent specific in active disease; titres correlate with activity and guide taper. Anti-BP230 ELISA is positive in 50 to 70 percent and tracks pruritus. Total IgE and eosinophil count are usually raised and predict biologic responsiveness. A bedside Tzanck smear from a bulla floor shows eosinophils (not the acantholytic keratinocytes of pemphigus).^[1]

Before any systemic therapy, run the baseline work-up: FBC, renal and liver function, HbA1c or fasting glucose, vitamin D, DEXA, chest radiograph, infection screening (TB, hepatitis B/C, HIV where rituximab or dupilumab is contemplated), G6PD activity if dapsone is planned, and vaccination status (influenza, pneumococcal, COVID-19, shingles).^[1]

Management — the topical-first paradigm

The modern paradigm is topical-first — the elderly cannot afford prolonged systemic steroids. Mortality in BP is driven less by the blisters than by steroid toxicity (infection, osteoporosis, diabetes, cardiovascular events, falls), so the field has shifted decisively toward steroid-sparing regimens.^[1][2]

First-line: potent topical clobetasol propionate 0.05 percent. In the pivotal randomized comparison, the standard regimen started at 40 g/day with tapering over 12 months, while a milder regimen of 10 to 30 g/day tapered over about 4 months achieved equally reliable blister control and, in moderate disease, nearly halved the risk of death or life-threatening adverse events — allowing a 70 percent reduction in cumulative topical-steroid exposure. Superpotent topical corticosteroids improve survival in BP and are effective even in extensive disease.^[14][2]

Plus doxycycline 200 mg daily as the steroid-sparing backbone. The BLISTER trial showed that starting doxycycline 200 mg/day is non-inferior to oral prednisolone 0.5 mg/kg/day for short-term blister control (three or fewer blisters at six weeks) and significantly safer in the long term — severe, life-threatening or fatal treatment-related events by one year occurred in 18 percent versus 36 percent of patients started on prednisolone.^[13][2] Layer in skin care and active comorbidity management from the outset — in the frail elderly, the treatment challenge is delivering enough immunosuppression to control blistering without the steroid toxicity that drives mortality.^[1][3]

^{[14] [13] [5] [19] [18]}

Second-line and refractory — steroids, then biologics

Oral prednisolone 0.5 mg/kg/day — the dose used as standard therapy in BLISTER — remains an option for moderate-to-severe BP when topical-first strategies fail, but cumulative exposure drives the mortality. Taper once control is achieved, guided by clinical activity and anti-BP180 NC16A ELISA values rather than a fixed schedule.^[13][16][3]

Steroid-sparing agents step in as prednisolone tapers: low-dose weekly methotrexate (a mean of 10 mg per week maintained remission in a large retrospective series combined with initial short-term superpotent topical steroids), azathioprine, mycophenolate mofetil and dapsone — aiming to reduce the cumulative steroid dose, as demonstrated for adjuvant doxycycline, dapsone and immunosuppressants in randomized studies.^[17][3]

Refractory disease now has three biologics. Rituximab (anti-CD20 B-cell depletion) achieves complete remission in about 70 percent of patients in the largest systematic review. Omalizumab (anti-IgE) achieves complete remission in about two-thirds of patients with refractory, often corticosteroid-dependent BP. Dupilumab (anti–IL-4Rα, blocking IL-4/IL-13 type 2 signalling) achieves complete remission in about two-thirds and is now in phase 2/3 evaluation in the LIBERTY-BP ADEPT trial.^[5][19][18]

Emerging agents — JAK inhibitors (upadacitinib, baricitinib) and anti-FcRn (efgartigimod) — have promising case-series evidence but are not yet first-line. The taper principle: control blistering, taper prednisolone first, let the steroid-sparing agent take effect, and track anti-BP180 NC16A titres every 3 months as a relapse biomarker.^[1][5]

Drug-induced BP — withdraw first

Stop the offending drug immediately. Consider drug causation in any new-onset BP — take a careful drug history including over-the-counter medications and recent vaccines. DPP-4 inhibitors are the commonest trigger in elderly type 2 diabetics (BP arises via altered antigen presentation of BP180 by dysregulated e-cadherin); checkpoint-inhibitor BP can be rapidly progressive and refractory and warrants multidisciplinary management with oncology.^[7]

Management combines withdrawal of the offending medication — the step that enables earlier recognition and control of drug-induced pemphigoid — with the same mainstay therapies as idiopathic BP: high-potency topical corticosteroids and systemic corticosteroids tailored to disease severity.^[7][3]

Special populations

The elderly and frail — the typical BP patient — make steroid toxicity the dominant risk. Prefer potent topical clobetasol plus doxycycline over oral prednisolone, give bone protection, and watch for infection, diabetes, cataracts, GI bleed and falls.^[2]

Parkinson's disease and neurological comorbidity bring shared BP180 epitopes, drug interactions, dysphagia and aspiration risk, and higher infection risk with steroids — active collaboration between dermatologist, neurologist and geriatrician is the rule.^[8]

Pemphigoid gestationis typically arises in the third trimester with pruritic urticarial plaques progressing to tense bullae, and is associated with HLA-DR3 (and DR3 with DR4). Management follows the same severity-guided escalation as BP outside pregnancy. There is a high risk of prematurity, and maternal IgG crosses the placenta — under 10 percent of newborns develop transient lesions. The condition is usually self-limiting within months of delivery but recurs in subsequent pregnancies.^[10][15]

Mucous membrane pemphigoid is treated by severity: mild-to-moderate disease starts with dapsone, methotrexate or tetracyclines plus or minus topical corticosteroids, while severe disease requires dapsone combined with cyclophosphamide plus or minus oral corticosteroids. Ocular involvement heals with scarring and can progress to blindness — urgent ophthalmology input is essential.^[4][12]

Prognosis and surveillance

BP can be self-limiting — remission within 1 to 5 years in many patients — but relapse occurs in 30 to 40 percent within a year of withdrawal. Morbidity and mortality are driven by treatment complications, associated neurological disease and frailty rather than the blistering itself; one-year mortality is 10 to 30 percent in the elderly, roughly two to six times age-matched controls.^[1][8]

Anti-BP180 NC16A titres track activity and guide taper. ELISA values correlate with disease activity over long-term follow-up, and in the classic monitoring study no relapse occurred when prednisolone was tapered after values had fallen to about 40 percent of baseline, even though they remained above the normal range.^[16]

Surveillance is clinical review plus anti-BP180 titres every 3 months in active disease or taper, and every 6 to 12 months in stable remission; annual DEXA, ophthalmology (for MMP or prolonged steroid use), blood pressure, glucose and lipids at each visit; and vaccination updates. Quality-of-life instruments (BPDAI for activity, ABSIS, ABQOL) inform step-up and step-down decisions.^[1]

Preventable harm

The mantra: topical first, doxycycline early, prednisolone sparingly, biologics for the refractory. BP kills the elderly through its treatment, not its blisters — so the lowest effective immunosuppression is the goal.^[1][2]

Ward-round test

^[1]

1. An 80-year-old with tense bullae, intense itch, negative Nikolsky. Histology: subepidermal split with eosinophils. DIF: linear IgG/C3 at the BMZ. Salt-split: epidermal binding. Name the antigen and the gold-standard test.^[1][3]

AnswerShowHide

The antigens are BP180 (collagen XVII, especially the NC16A domain) and BP230 (BPAG1) at the basement membrane zone. The gold-standard diagnostic test is direct immunofluorescence of perilesional skin showing linear IgG4/C3 along the BMZ — contrast with pemphigus, which is intercellular chicken-wire IgG4.^[1][3]

2. Same patient. The registrar wants to start prednisolone 1 mg/kg/day. What trial argues against that as first-line, and what do you start instead?^[2][13]

AnswerShowHide

The BLISTER trial showed doxycycline 200 mg daily non-inferior to prednisolone 0.5 mg/kg/day for short-term control, with fewer severe, life-threatening or fatal events at one year. Start potent topical clobetasol (about 40 g/day initially) plus doxycycline 200 mg daily — the elderly cannot afford prolonged systemic steroids.^[13][14]

3. DIF shows linear IgG at the BMZ, but the salt-split test binds the DERMAL floor. Re-diagnose and name the antigen.^[1]

AnswerShowHide

Epidermolysis bullosa acquisita (EBA) — the BED rule: Bullous pemphigoid binds the epidermal roof, EBA binds the dermal floor. The antigen is type VII collagen (anchoring fibrils). EBA is mechanobullous with milia and scarring, refractory to steroids; confirm with type VII collagen ELISA or immunoblot.^[1]

4. A 72-year-old diabetic started vildagliptin nine months ago now has new tense bullae. What is the diagnosis, the first action, and the drug rule on rechallenge?^[7]

AnswerShowHide

Drug-induced BP from the DPP-4 inhibitor. Stop the gliptin immediately and switch to an alternative class (e.g., an SGLT2 inhibitor). Drug rechallenge is contraindicated in gliptin-induced BP; disease often resolves within weeks to months of withdrawal.^[7]

5. A 30-year-old woman at 32 weeks gestation has periumbilical urticarial plaques progressing to bullae. Diagnosis, antigen, and the two obstetric priorities?^[10][11]

AnswerShowHide

Pemphigoid gestationis, driven by antibodies to BP180 — the same hemidesmosomal protein targeted in bullous pemphigoid. The obstetric priorities are vigilance for prematurity (obstetric co-management) and awareness that maternal IgG crosses the placenta — under 10 percent of newborns develop transient lesions. Anticipate recurrence in subsequent pregnancies; treat with the same severity-guided escalation as BP outside pregnancy.^[10][15]

References19ShowHide

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