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 applied to all affected and clinically uninvolved skin, around 30 to 40 g/day total-body application in adults, tapering over weeks to months. It is surprisingly effective even in moderate-to-severe BP and halves cumulative systemic-steroid exposure.[2]

Plus doxycycline 200 mg daily (100 mg BD) ± nicotinamide 500 mg TDS as steroid-sparing. Doxycycline works through anti-inflammatory and anti-protease (MMP-9 inhibition) effects at sub-antimicrobial dose. The BLISTER trial showed doxycycline non-inferior to prednisolone 0.5 mg/kg/day for short-term control, with significantly fewer serious adverse events and fewer deaths at one year.[2][5]

Layer in skin care (antiseptic/emollient), bone protection (calcium 1 g plus vitamin D 800 to 1000 IU daily; bisphosphonate if over 7.5 mg/day prednisolone is anticipated beyond 3 months), comorbidity management, and vaccination before immunosuppression.[1]

[1] [5]

Second-line and refractory — steroids, then biologics

Oral prednisolone 0.5 to 0.75 mg/kg/day (up to 1 mg/kg/day in extensive disease) is for moderate-to-severe BP failing topical clobetasol and doxycycline. Taper once control is achieved — reduce by 5 to 10 mg every 2 weeks to 20 mg/day, then 2.5 mg every 2 to 4 weeks to 10 mg/day, then 1 mg every 2 to 4 weeks — aiming to discontinue within 6 to 9 months. Monitor blood pressure, glucose, electrolytes, bone density, weight and infection at each visit.[3]

Steroid-sparing agents step in as prednisolone tapers: methotrexate 10 to 25 mg weekly (with folic acid), azathioprine 1 to 3 mg/kg/day (TPMT genotyping first), mycophenolate mofetil 1 to 1.5 g BD, and dapsone 50 to 100 mg daily (check G6PD; monitor methaemoglobin, reticulocytes and LFTs — best in neutrophil- or eosinophil-rich variants).[3][5]

Refractory disease now has three biologics. Rituximab 1 g IV two doses 14 days apart (anti-CD20 B-cell depletion) achieves around 70 percent complete remission in the largest systematic review. Omalizumab 300 to 600 mg subcutaneously every 4 weeks (anti-IgE) is particularly effective when total IgE is elevated and pruritus is prominent, working within 4 to 12 weeks. Dupilumab 600 mg loading then 300 mg every 2 weeks (anti-IL-4Rα, blocking the Th2 axis) met all primary and key secondary endpoints in the LIBERTY-BP ADEPT trial of 2024, with patients roughly five times more likely to reach sustained remission. IVIG 2 g/kg/month is an adjunct for refractory or infection-prone patients.[5]

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]

Treatment is topical clobetasol ± a short course of prednisolone 0.25 to 0.5 mg/kg/day; disease usually resolves after withdrawal but may recur on rechallenge. Drug rechallenge is contraindicated in gliptin-induced BP; switch to an alternative class such as an SGLT2 inhibitor.[1][7]

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 is managed with potent topical steroids and prednisolone 0.5 to 1 mg/kg/day for extensive disease — systemic steroids are safer here than in older adults because the patient is young. HLA-DR3 and HLA-DR4 are associated; fetal risk (preterm delivery, small-for-gestational-age, transient neonatal BP from placental IgG transfer) demands obstetric co-management. The condition usually remits postpartum but recurs in subsequent pregnancies, often earlier and more severe.[10][11]

Mucous membrane pemphigoid is treated more aggressively from the outset — prednisolone plus a steroid-sparing agent — and ocular involvement is an emergency: urgent ophthalmology for symblepharon release to prevent blindness. Paediatric BP is rare, usually localised (genital in girls, perioral), and treated with low-dose topical steroids, resolving within months. In hepatic or renal impairment, MMF is contraindicated, azathioprine and dapsone are dose-reduced, and methotrexate is contraindicated when eGFR is under 30 mL/min.[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. A 50 percent reduction in titre is associated with clinical remission in about 80 percent and informs tapering decisions; persistent or rising titres predict relapse. Relapse predictors are high baseline titre (over 200 U/mL), older age, multi-drug immunosuppression, late tapering, neurological comorbidity and persistent IgE elevation.[1]

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]

Answer

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]

Answer

The BLISTER trial showed doxycycline 200 mg daily non-inferior to prednisolone 0.5 mg/kg/day for short-term control, with fewer serious adverse events and deaths at one year. Start potent topical clobetasol 30 to 40 g/day total-body plus doxycycline 200 mg daily ± nicotinamide — the elderly cannot afford prolonged systemic steroids.[2]

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

Answer

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]

Answer

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]

Answer

Pemphigoid gestationis, anti-BP180 NC16A. The obstetric priorities are serial fetal growth scans (risk of preterm delivery and small-for-gestational-age from placental IgG transfer) and anticipation that it recurs in subsequent pregnancies, often earlier and more severe. Treat with potent topical steroids ± prednisolone 0.5 to 1 mg/kg/day.[10][11]

References

1. [1]Akbarialiabad H, Schmidt E, Patsatsi A, et al. Bullous pemphigoid Nat Rev Dis Primers, 2025.PMID 39979318
2. [2]Bernard P, Antonicelli F. Bullous Pemphigoid: A Review of its Diagnosis, Associations and Treatment Am J Clin Dermatol, 2017.PMID 28247089
3. [3]Miyamoto D, Santi CG, Aoki V, et al. Bullous pemphigoid An Bras Dermatol, 2019.PMID 31090818
4. [4]Schmidt E, Rashid H, Marzano AV, et al. European Guidelines (S3) on diagnosis and management of mucous membrane pemphigoid, initiated by the European Academy of Dermatology and Venereology - Part II J Eur Acad Dermatol Venereol, 2021.PMID 34309078
5. [5]Cao P, Xu W, Zhang L. Rituximab, Omalizumab, and Dupilumab Treatment Outcomes in Bullous Pemphigoid: A Systematic Review Front Immunol, 2022.PMID 35769474
6. [6]Moro F, Fania L, Sinagra JLM, et al. Bullous Pemphigoid: Trigger and Predisposing Factors Biomolecules, 2020.PMID 33050407
7. [7]Verheyden MJ, Bilgic A, Murrell DF. A Systematic Review of Drug-Induced Pemphigoid Acta Derm Venereol, 2020.PMID 32176310
8. [8]Grotewold N, Albin RL. Update: Protective and risk factors for Parkinson disease Parkinsonism Relat Disord, 2024.PMID 38879999
9. [9]Pratasava V, Sahni VN, Suresh A, et al. Bullous Pemphigoid and Other Pemphigoid Dermatoses Medicina (Kaunas), 2021.PMID 34684098
10. [10]Al-Fouzan AW, Galadari I, Oumeish I, et al. Herpes gestationis (Pemphigoid gestationis) Clin Dermatol, 2006.PMID 16487884
11. [11]Agostinis P, Antonello RM. Pemphigoid Gestationis N Engl J Med, 2020.PMID 32846065
12. [12]Du G, Patzelt S, van Beek N, et al. Mucous membrane pemphigoid Autoimmun Rev, 2022.PMID 34995762