Background The clinical condition generalized epidermolytic hyperkeratosis, also known as bullous congenital ichthyosiform erythroderma, is an autosomal dominant disorder and presents as a bullous disease of the newborn followed by an ichthyotic skin disorder throughout life. Clinical epidermolytic hyperkeratosis (cEHK) has characteristic histopathologic findings. Mosaic cEHK, which occurs without a family history, is a sporadic condition that clinically resembles epidermal nevi but demonstrates histopathologic findings similar to the generalized disorder; when a post zygotic mutation involves the germ line, the disease can occur in subsequent generations as generalized cEHK. Ichthyosis Bullosa of Siemens (IBS) is similar histopathogically, but clinically distinct from generalized cEHK, presenting with more superficial bullae. Objectives It is well established that the clinical diagnoses generalized cEHK, mosaic cEHK, and IBS have similar histopathologic findings of epidermolysis with hyperkeratosis. We sought to characterize a) the spectrum of histopathologic features and b) to assess whether there were histopathologic differences between these clinically distinct disorders. Methods One hundred seventeen skin biopsy slides from the National Registry for Ichthyosis and Related Skin Disorders were reviewed blinded to clinical information. All slides were systematically evaluated for a variety of features including differences in the pattern of the epidermolysis and hyperkeratosis. Clinical predictions of whether the biopsy was obtained from patients with generalized cEHK, mosaic cEHK, or IBS were made based on the histologic pattern of the epidermolysis and hyperkeratosis. Results Eighteen of the one hundred seventeen slides revealed features sufficient to make a histologic diagnosis of epidermolytic hyperkeratosis (hEHK). One additional slide, for which a definitive histologic diagnosis was not possible, had features of both hEHK and acantholytic dyskeratosis. Two distinct patterns of the histopathologic changes were observed within the eighteen slides diagnostic of hEHK, a) continuous involvement of the entire horizontal epidermis and b) focal involvement revealing skip areas of normal appearing epidermis along the horizontal epidermis. Upon clinical correlation, all twelve of the slides with continuous involvement were from patients with generalized cEHK. One slide was from acral skin and had continuous involvement. This was from a patient with Vorner’s palmoplantar keratoderma. Of the remaining five slides with focal involvement, two patterns were observed; focal involvement of both the granular and spinous layers and focal involvement of only the granular layer. The three slides with focal involvement of the granular and spinous layer were from patients with mosaic cEHK. Of the two slides with focal involvement confined to the granular layer, one was from a patient with IBS and the other from a patient with generalized cEHK. Limitation The sample pool is biased by who was enrolled in the registry an...

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A 25‐year‐old Micronesian man from the island of Otia developed erythematous plaques on his legs. He was diagnosed with erythema nodosum and treated with systemic prednisone. Two months later, he presented with erythematous nodules on his forehead, cheeks, and chin (Fig. 1). Examination revealed scattered violaceous papules on his chest, arms, forearms, hands, and feet, and deep purple macules on his palms and soles. Laboratory evaluation included negative serologies for human immunodeficiency virus, rapid plasma reagin, and hepatitis A, B, and C. 1 Erythematous papules and nodules cover the forehead, nose, cheeks, chin, and ears Routine histopathology revealed nodular aggregates of histiocytes, plasma cells, and lymphocytes. Histiocytes showed basophilic clusters of organisms within vacuoles, suggesting globi. Acid‐fast stain revealed numerous acid‐fast‐positive rod‐shaped organisms. The bacterial index on the Fite stain was four (bacterial index/Ridley's logarithmic scale, indicating 10–100 bacteria/high power field) (Fig. 2). An acid‐fast stain obtained from a smear of tissue was positive for acid‐fast bacilli, but no acid‐fast bacilli were cultured. 2 The bacterial index on the Fite stain was four After the first day of treatment with dapsone 100 mg, rifampin 600 mg, and clofazimine 50 mg, the patient complained of burning and pain in his ankles and wrists. There was intense erythema within the lesions. Edema developed in his hands and feet. Consultation with the Gillis W. Long Hansen's Disease Center in Carville, Louisiana, recommended prompt treatment with corticosteroids. The edema of the hands and wrists was treated as a type I reversal reaction with prednisone 1 mg/kg/day. Subsequently, the edema and neuralgia quickly resolved in his distal extremities.