Vesiculobullous Disorders of the Oral Cavity
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Direct answer
Intraoral blisters rarely survive intact — the fragile oral epithelium shears them into flaccid, ragged ulcers — so the vesiculobullous diseases are diagnosed by their cleavage plane and immunofluorescence rather than by seeing a bulla. Pemphigus vulgaris, driven by autoantibodies against desmoglein 3, splits the epithelium suprabasally, gives a positive Nikolsky sign, shows acantholytic Tzank cells on cytology and a fishnet intercellular IgG pattern on direct immunofluorescence, and commonly begins in the mouth before the skin. Mucous membrane pemphigoid, directed at the basement membrane zone (BP180 antigen), splits subepidermally, produces desquamative gingivitis and scarring of the conjunctiva, and deposits a continuous linear band of IgG or C3 along the basement membrane. Erythema multiforme, usually a hypersensitivity reaction to herpes simplex or drugs, adds target lesions and blood-crusted lips.
What you must remember
- The master discriminator: level of split — intraepithelial/suprabasal (pemphigus group) versus subepithelial/sub-basilar (pemphigoid group, erythema multiforme, linear IgA disease); every other finding hangs off this single histological fact.
- Pemphigus vulgaris: IgG against desmoglein 3 (with desmoglein 1 overlap in mucocutaneous disease); oral lesions precede skin in over half of patients; flaccid blisters rupture instantly leaving broad, tender ulcers; positive Nikolsky sign; suprabasal clefting with acantholytic (Tzank) cells; DIF shows intercellular fishnet IgG and C3.
- Mucous membrane pemphigoid: antibodies against BP180 (and BP230) at the basement membrane zone; desquamative gingivitis is the oral signature; tense skin bullae; scarring conjunctivitis defines the disease; DIF shows a smooth continuous linear IgG or C3 band.
- Bullous pemphigoid: elderly patients, large tense cutaneous bullae, oral involvement mild and late; linear IgA disease mirrors it with IgA deposition and childhood and adult forms.
- Erythema multiforme and Stevens-Johnson syndrome: hypersensitivity to herpes simplex reactivation or drugs (sulphonamides, anticonvulsants, NSAIDs); target lesions on skin, haemorrhagically crusted lips, abrupt widespread oral ulceration, self-limiting over weeks; recurrent forms track HSV.
- Dermatitis herpetiformis and epidermolysis bullosa: gluten-associated granular IgA at dermal papillae in the former; inherited mechanobullous disease with scarring oral involvement in the latter.
- Management principles: twin biopsies — histology plus fresh-frozen tissue for direct immunofluorescence; Tzank smear as a rapid adjunct; systemic corticosteroids with sparing agents guided by dermatology; topical steroids and hygiene as dental adjuncts.
Two patients, two planes of separation
A 42-year-old woman has three months of painful, widespread oral ulceration; erosions now involve the scalp. Step one, examine for the dynamic signs: lateral pressure on apparently normal buccal mucosa shears the epithelium away — a positive Nikolsky sign pointing to pemphigus. Step two, the twin biopsies: perilesional histology shows a suprabasal split with acantholytic cells, and the specimen for direct immunofluorescence shows intercellular IgG in a fishnet pattern — pemphigus vulgaris, desmoglein 3 disease. Step three, the Tzank smear shows rounded acantholytic cells with large nuclei, confirming intraepithelial separation at the bedside. Step four, begin systemic therapy with the dermatologist — corticosteroids tapered with a sparing agent — with dental support: chlorhexidine, topical steroids and treatment of secondary Candida. Step five, monitor steroid complications.
Contrast her with a 58-year-old woman whose gingivae are diffusely red, peeled and tender — desquamative gingivitis. Her Nikolsky sign may be positive too, so histology decides: a subepithelial split, with linear continuous IgG and C3 along the basement membrane — mucous membrane pemphigoid. Her management differs in one decisive respect: urgent, lifelong ophthalmological surveillance, since the eye, not the mouth, blinds these patients.
Where examiners set the trap
The question almost always resolves to pemphigus versus pemphigoid, and the safe answering grid is four rows: split level (suprabasal versus subepithelial), autoantigen (desmoglein 3 versus BP180), blister quality (flaccid versus tense), and DIF pattern (fishnet intercellular versus linear basement-membrane band). The Nikolsky sign is the second trap — positive in pemphigus but also frequently in pemphigoid and erythema multiforme, so it selects within a differential rather than clinching one. The third is the site emphasis: pemphigus vulgaris is commonest in Indian dermatovenerology practice among the immunobullous diseases and is very often oral-first, so a dentist may genuinely be the first diagnostician — an exam-ready sentence. The fourth is erythema multiforme's suddenness, crusted bloody lips and self-limiting course, contrasted with the chronicity of pemphigus; and recurrent disease triggers HSV history-taking and antiviral prophylaxis.
Frequently asked questions
Which antibody and split define pemphigus vulgaris?
IgG autoantibodies against desmoglein 3 cause suprabasal intraepithelial cleavage with acantholysis, producing flaccid blisters and a positive Nikolsky sign.
What DIF pattern distinguishes pemphigoid from pemphigus?
Pemphigoid shows a continuous linear band of IgG or C3 along the basement membrane zone, versus pemphigus's intercellular fishnet deposition of IgG.
Why is mucous membrane pemphigoid an ophthalmological emergency risk?
Subepithelial blistering of the conjunctiva scars and forms symblephara, progressively endangering vision — the complication that defines the disease's severity.
What triggers erythema multiforme most often?
Reactivation of herpes simplex virus and reactions to drugs such as sulphonamides, anticonvulsants and NSAIDs; recurrent disease classically follows HSV episodes.
What is a Tzank smear and what does it show?
A cytological smear from the base of a fresh erosion showing rounded acantholytic cells — rapid bedside support for pemphigus.