An Unusual, Delayed, Localized Bullous Reaction After Subcutaneous Allergen Immunotherapy

Abstract

C. Left arm Cat (10,000 BAU/mL) 6 3000 AU 2400 AU Dog (1:20) 2 0.1 mL 0.08 mL Phenolated buffered 2 N/A N/A A 19-year-old man with a history of allergic rhinoconjunctivitis and who was receiving monthly subcutaneous allergen immunotherapy (SCIT) presented with an unusual delayed local reaction. The patient had previously tolerated 17 months of SCIT buildup and 3 months of maintenance immunotherapy in 3 separate injections (Tables I and II) with only large local reactions. In this instance, he had large local reactions approximately 1 hour after injections (2 in the right arm 5 cm apart and 1 in the left arm). Six to 7 hours later, he noticed multiple vesicles on the right arm just below the lower injection site. The patient returned to our clinic with bullous lesions at this site approximately 24 hours after inoculation with 0.4 mL of a 1:1 concentration of extract that contained weeds, ragweed, molds, and dust mites (Tables I and II) near the end of our ragweed season. He had received the same dose the previous month due to a large, painful local reaction from his prior maintenance dose of 0.5 mL. The patient had severe pruritus around the bullae and no tenderness, burning, or any systemic symptoms. There were no associated extrinsic factors on the day of presentation (physical exercise, trauma, or concomitant viral infection) or before the injections. He had no recent travel. His medical history was significant for unspecified mitochondrial metabolism disorder. There was no prior personal or family history of bullous dermatitis. He was not taking any medications known to cause bullae, nor was he using any topical medications. Results of a physical examination were significant for a 10 10-mm bulla just inferior to the lower injection site, and below this was a larger 25 25-mm bulla with surrounding erythema, which measured 31 33 mm (Figure 1). The differential diagnosis included infection, such as bullous impetigo, and delayed local hypersensitivity reaction. The patient was started on cephalexin 500 mg twice daily for 10 days and prednisone 40 mg once daily for 3 days. The following day, Dermatology lanced the bullae, and fluid was sent for Gram stain and culture. Results of the Gram stain showed no organisms. The culture eventually showed no growth. No skin biopsy was obtained. When the patient was evaluated 1 month saline solution