Case Report: A Bullous Eruption

Figure 2. The patient had palpable purpura and hemorrhagic vesicles of both legs, with tender erythematous plaques and swelling over the feet.

Dermatologic findings can present in 40–60% of patients with EGPA, with palpable purpura being the most common manifestation.¹ Non-hemorrhagic bullae are an exceedingly rare cutaneous manifestation of EGPA. Four cases we found described bullae as the initial cutaneous manifestation of EGPA, one as a relapsing feature and another in a patient with overlapping EGPA and cryoglobulinemic vasculitis.^2-5,7,8 EGPA is typically not considered in the differential diagnosis of patients presenting with non-hemorrhagic bullae unless other clinical features are present.

Interestingly, four cases of EGPA-Wells syndrome overlap presented with non-hemorrhagic bullae.⁹ Wells syndrome is a rare form of non-infectious cellulitis with histological findings of eosinophilic dermal infiltration and flame figures (i.e., collagen fibers coated with eosinophilic degranulation products). All of the cases had clinical features of both Wells syndrome and EGPA. Our patient did not present with pseudocellulitis, nor did she have flame figures on biopsy.

The mechanism of blister formation in EGPA remains unclear. Eosinophilic dermal infiltration, followed by the release of eosinophilic granule proteins, such as major basic protein (MBP), eosinophil-derived neurotoxin and eosinophil cationic protein, has demonstrated a role in the pathogenesis of other blistering diseases, such as bullous pemphigoid.¹⁰

In vitro addition of α2-macroglobulin, which inhibits MBP, was shown to block dermal-epidermal separation.¹¹ A similar mechanism may explain the development of bullae in EGPA. This mechanism could also explain the common finding of bullae in EGPA-Wells syndrome overlap because Wells syndrome is associated with marked inflammatory changes from eosinophilic degranulation.

In Sum

We describe a rare case of EGPA pre­senting as a non-hemorrhagic bullous eruption with peripheral eosinophilia. The patient was initially thought to have either a drug reaction or a primary immunobullous disorder, and this drove initial investigations and management. EGPA was suspected only after she developed microvascular hemorrhages and purpura. Although rare, EGPA should be kept in the differential diagnosis of patients presenting with non-hemorrhagic bullae if prodromal features of EGPA, such as adult-onset asthma and otolaryngologic symptoms, are present.

Jordan Friedmann, MD, is a PGY-3 internal medicine resident at the University of British Columbia, Vancouver, and is planning on pursuing a career in rheumatology.

Julia Tan, MD, is a PGY-5 rheumatology resident at the University of British Columbia.

Danny Mansour, MD, is a PGY-4 dermatology resident at the University of British Columbia. He is the co-chair of the Canadian Dermatology Association Resident and Fellows Society, where he has organized and led nationwide dermatology curricula. He is the chief resident for the January–June 2022 term and has a strong interest in medical education.

Sheila Au, MD, FRCPC, is a clinical associate professor in the Department of Dermatology and Skin Science at the University of British Columbia. She is an active member of the Canadian Dermatology Association’s Canadian Rheumatology and Dermatology Working Group and served as an associate editor of the Journal of Cutaneous Medicine and Surgery. Dr. Au received the 2019 Practitioner of the Year Award from the Dermatology Society of British Columbia.

Neda Amiri, MD, FRCPC, is clinical assistant professor in the Division of Rheumatology at the University of British Columbia, as well as the director of the PReDICT (Pregnancy and Rheumatic Disease Clinic) clinic at Mary Pack Arthritis Centre and a consultant in the Lupus Clinic. She attended internal medicine and rheumatology training at the University of British Columbia.

Acknowledgments

We thank Hamid Masoudi, MD, FRCPC, staff pathologist at St. Paul’s Hospital, Vancouver, for his assistance reviewing the pathology.

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