Differential diagnosis
Many diseases manifest with bullae/vesicles. Workup should begin with a complete history and physical exam. A skin biopsy may be needed to make a definitive diagnosis.
Herpes zoster typically manifests with clustered pruritic vesicular lesions on a red base that follow a dermatomal distribution. Pemphigus vulgaris appears with flaccid blisters, erosions, and tend to have oral mucosal lesions. A positive Nikolsky’s sign is characteristic of pemphigus vulgaris. Bullous impetigo appears with scattered lesions of erythema and macules, progressing to thin roofed bullae and subsequently to “honey-crusted” lesions. In toxic epidermal necrolysis, the bullae are widespread and lead to sloughing of the skin. Pyoderma gangrenosum has ulcer formation preceded by pustules that typically expand rapidly to approximately 20 cm. These ulcers have necrotic bluish edges.
Diagnostic test results
The patient’s herpes culture was negative. Fortunately, the punch biopsy was sent for direct immunofluorescence. Direct immunofluorescence showed positive staining with immunoglobulin (Ig) G in the intercellular regions of the epidermis and no staining with IgA, IgM, C3, or fibrinogen. Hematoxylin and eosin-stained sections showed suprabasal blistering containing neutrophils and a few eosinophils. These results are consistent with pemphigus vulgaris.