Vesiculobullous Disorders — Pemphigus, Pemphigoid and Diagnostic Patterns

Start with the level of the split. Pemphigus separates keratinocytes within the epidermis, while bullous pemphigoid separates the epidermis from the underlying dermis. The split determines the strength of the blister roof, the appearance of the lesion and the expected biopsy findings. It also directs you towards the relevant adhesion structure: desmosomes or hemidesmosomes.

Then combine the clinical clues: flaccid or tense blisters, painful oral erosions or prominent itch, and the expected immunofluorescence pattern. No single finding should carry the entire diagnosis. An eroded lesion may no longer look like an intact blister, and an immunofluorescence result answers a different question from an ordinary histology image.

Use a chain you can reproduce in either direction: target → adhesion failure → split level → blister appearance → immunofluorescence. If an image shows epidermal intercellular staining, return to desmosomal antibodies and pemphigus. If a clinical stem describes an older person with intensely itchy tense bullae, consider bullous pemphigoid and look for confirmation at the basement membrane.

The words pemphigus and pemphigoid sound similar because both describe blistering disorders. Their target structures differ. Desmosomes link neighbouring keratinocytes; hemidesmosomal adhesion anchors basal keratinocytes to the basement-membrane region. This anatomical distinction accounts for the different split levels and is more reliable than memorising the two names as an isolated pair.

In a combined stem, use the table as a consistency check. Oral erosions, fragile blisters, suprabasal acantholysis and intercellular staining reinforce one another. Itch, tense bullae, a subepidermal cavity and a linear basement-membrane pattern reinforce the other diagnosis. If a clue disagrees, examine whether the specimen, stain or clinical context has been described differently.

Desmogleins are adhesion proteins in desmosomes. Pemphigus vulgaris involves IgG directed against desmoglein 3, often with desmoglein 1 as well. The antibodies impair keratinocyte adhesion, producing acantholysis. Acantholysis means loss of cohesion between epidermal cells; it describes the structural result and should be distinguished from the antibody target itself.

Clinical pemphigus vulgaris often begins with painful oral erosions. Skin lesions can follow, although some patients have predominantly mucosal disease. The fragile roof means intact bullae may be less obvious than erosions. A vignette with persistent painful oral ulcer-like lesions followed by easily ruptured skin blisters therefore fits the disease even if the photograph shows mostly denuded areas.

Pemphigus foliaceus principally targets desmoglein 1 near the upper epidermis. Its superficial blisters rupture quickly and can appear as crusted or scaly erosions. Oral mucosa is usually spared. Do not identify foliaceus just because the word pemphigus appears: distinguish superficial skin disease from the oral-plus-skin pattern of vulgaris.

A positive Nikolsky sign describes epidermal separation with gentle lateral pressure on clinically normal-appearing or perilesional skin. It reflects tissue fragility and is classically associated with pemphigus. In typical bullous pemphigoid it is negative because the epidermal roof remains cohesive even though its attachment to the underlying tissue is disrupted.

The sign supports a mechanism; it is not an antibody assay. A question can ask about the bedside sign, the level of the split or the diagnostic test, and these require different answers. For bedside fragility choose Nikolsky. For loss of keratinocyte cohesion choose acantholysis. For demonstration of deposited immunoreactants choose direct immunofluorescence.

Avoid making Nikolsky positivity synonymous with pemphigus in every setting. Other causes of epidermal fragility belong in the wider differential, especially when the stem describes systemic illness, a recent drug exposure or widespread epidermal loss. Use the surrounding presentation and biopsy findings to decide whether an autoimmune blistering disorder is the intended diagnosis.

Pemphigus vulgaris shows suprabasal acantholysis. The split lies above the basal layer, and basal keratinocytes remain along the basement membrane, creating the familiar row of tombstones appearance. The phrase refers to retained basal cells rather than to cells floating within the blister. First identify the cavity, then determine whether a basal layer remains beneath it.

Bullous pemphigoid produces a subepidermal blister. The full epidermal thickness forms the roof. Eosinophils can be present in the dermis and blister cavity. If the whole epidermis has lifted off the underlying dermis, do not call the cavity suprabasal merely because it appears near the basal layer at low magnification.

Routine histology establishes architecture, but architecture alone may not identify the precise autoimmune disease. Several disorders can produce a subepidermal split. Immunofluorescence and antigen-specific tests provide additional discrimination. In an image question, describe what the stain actually demonstrates rather than supplying a remembered antibody name unsupported by that particular image.

In direct immunofluorescence, labelled reagents identify immunoreactants already deposited in the patient’s tissue. Pemphigus vulgaris shows intercellular epidermal IgG in a net-like or chicken-wire pattern. Bullous pemphigoid shows a linear band of IgG and C3 at the basement-membrane zone. Locate the staining before interpreting its shape.

Indirect immunofluorescence examines circulating serum antibodies using a suitable substrate. Antigen-specific ELISA can detect desmoglein antibodies in pemphigus or BP antigen antibodies in pemphigoid. These tests complement rather than rename the tissue findings. A serum antibody test and a direct tissue fluorescence image should not be described as though they were the same procedure.

For a fast visual answer, ask where the light is: around epidermal cells or along the epidermal base. The net maps to cell-to-cell adhesion; the line maps to the basement-membrane region. This geographical approach connects the image to the target structure and helps you avoid confusing any bright linear signal elsewhere in a tissue section with the relevant diagnostic pattern.

Bullous pemphigoid antibodies recognise BP180, also called BPAG2 or type XVII collagen, and BP230, also called BPAG1. These are components of basal keratinocyte adhesion. Antibody binding triggers inflammatory injury, including complement activation and inflammatory-cell recruitment, which damages the dermal-epidermal junction and produces a subepidermal cavity.

A salt-split substrate separates skin through the lamina lucida. In the classical pattern, bullous pemphigoid antibodies localise to the epidermal side, often called the roof. Epidermolysis bullosa acquisita localises to the dermal side, or floor. This adds localisation within the basement-membrane region when a simple subepidermal blister or linear pattern is insufficient.

1. Take a lesional specimen suitable for routine histology so that the blister edge and split level can be assessed.
2. Take a separate perilesional, uninvolved specimen for direct immunofluorescence.
3. Place the histology specimen in formalin; use the laboratory’s appropriate transport medium for fluorescence.
4. Tell the laboratory the clinical suspicion and distinguish the two specimens clearly.

The distinction between the samples is a common procedural trap. Formalin is appropriate for the routine histology specimen, but the fluorescence specimen requires its own transport conditions, such as Michel medium where advised. Putting both samples in the same routine container can prevent the intended immune-deposition assessment. The diagnostic plan should therefore be organised before the biopsy.

If the first study is inconclusive, review the sample site, tissue preservation and clinical differential. A non-diagnostic specimen should not automatically erase a coherent clinical suspicion. Conversely, a supportive antibody result should be interpreted with the lesion pattern. For revision, connect each investigation to its purpose: architecture, deposited immunoreactants or circulating target-specific antibodies.

Pemphigus management aims to suppress disease activity and allow erosions to heal while limiting treatment toxicity. Rituximab with corticosteroids is a preferred first-line approach in moderate-to-severe pemphigus. Other immunosuppressive approaches depend on the patient and specialist plan. Do not present systemic corticosteroids alone as the only contemporary treatment option for every severity of disease.

Bullous pemphigoid treatment depends on extent, frailty and comorbidities. Potent topical corticosteroids are important, while systemic corticosteroids may be required for more extensive disease. Doxycycline-based strategies and other treatments can be considered in selected patients. A useful exam answer should identify the disease and management principle without inventing a universal dose or escalation schedule.

Supportive care includes wound care, pain control, assessment of oral intake and surveillance for infection. Oral disease can impair nutrition, while widespread erosions increase the burden of skin care. Before answering a drug question, determine whether the stem concerns pemphigus or pemphigoid: similarly sounding names do not imply an identical treatment strategy or identical risk profile.