Make the Diagnosis

A 72-year-old with an acute, pruritic, bullous eruption involving his right pretibial extremity

Publish date: July 9, 2020

A 72-year-old male with no significant past medical history presented with a 4-week history of an acute, pruritic, bullous eruption involving his right pretibial extremity. Examination revealed well-demarcated, erythematous plaques with tense bullae and erosions limited to the left lower leg, ankle, and dorsal foot. The rash was not preceded by any obvious trauma, insult, or chronic lower-extremity edema. The patient denied any new medications or exposures. He reported the lesions developed after a small scratch while playing tennis. Prior treatment with topical antibiotics and a brief course of oral antibiotics led to minimal improvement.

Localized bullous pemphigoid

Bullous pemphigoid is a systemic, autoimmune bullous disease that classically presents as widespread urticarial plaques or tense bullae with a predilection in the elderly population.¹

Localized variants of bullous pemphigoid (BP) are rare and have been reported to arise at sites of mechanical trauma, prior radiation, lymphedema, surgical scars, burns, fistulas, and ostomies.^1-3 Although the mechanism remains unclear, the Koebner phenomenon is thought to induce dysregulation of immunologic and vascular factors in sites of mechanical shear and trauma in susceptible individuals.³

Localized BP is an important entity for the dermatologist to be familiar with, as the diagnosis is often delayed. The localized, well-defined skin lesions frequently mimic contact dermatitis. In fact, previous reports have shown the most likely misdiagnosis of localized BP is acute allergic contact dermatitis, stasis dermatitis, and eczematous dermatitis.^4,5

Dr. Elizabeth H. Cusick

In this patient, histopathologic examination of a biopsy revealed a subepidermal blister with numerous eosinophils. Direct immunofluorescence study of perilesional skin showed strong linear IgG and C3 deposits at the basal membrane level. Serum level of autoantibody to BP180 antigen was elevated. Bacterial culture was positive for Staphylococcus aureus. These findings were suggestive of unilateral, localized BP with superimposed bacterial infection. Initial treatment with an extended course of doxycycline 200 mg twice daily, topical triamcinolone 0.1% ointment twice daily with compression therapy, and leg elevation led to clinical improvement with healing of previous lesions on the leg. At follow-up 3 weeks later, the patient had continued to develop new bullous lesions on the trunk and upper thighs. He was subsequently started on systemic immunosuppressive therapy for generalized bullous pemphigoid.

Dr. Lindsey Dolohanty

Importantly, localized BP generally follows a more benign disease course, although long-term follow-up is recommended for monitoring given the potential risk of developing the generalized form of BP of approximately 15%.3 Topical corticosteroids and oral antibiotics are recommended as the first-line therapy in these patients, with an escalated systemic therapy if needed for disease progression.^3,5

Our case represents an important differential diagnosis to consider when evaluating an acute localized bullous eruption in an elderly patient.

Dr. Cusick and Dr. Dolohanty are with the department of dermatology, University of Rochester (N.Y.), and provided the case and photo. Donna Bilu Martin, MD, edited the column.

Dr. Donna Bilu Martin

Dr. Bilu Martin is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at mdedge.com/dermatology. To submit a case for possible publication, send an email to dermnews@mdedge.com.