The biopsy revealed abundant lymphocytes, neutrophils, and eosinophils consistent with a diagnosis of cutaneous B cell pseudolymphoma. The pseudolymphoma was caused by an exaggerated response to a tick bite.
As the name implies, B cell pseudolymphomas clinically and histologically mimic the various patterns of cutaneous lymphoma, often appearing as a firm, pink to dark violet nodule. A biopsy is mandatory to distinguish between pseudolymphoma and true lymphoma. There is an association between pseudolymphomas and Borrelia burgdorferi, the organism responsible for Lyme disease. Thus, testing for Lyme disease is recommended for patients with pseudolymphomas who live in endemic areas. Patients who test positive should be treated with doxycycline 100 mg bid for 10 days.
In the absence of Lyme disease, a pseudolymphoma may resolve spontaneously over weeks or months. Resolution can be hastened with topical superpotent steroids, intralesional steroids, or systemic steroids. Treatment can begin with topical clobetasol 0.05% bid. If the lesion does not resolve, the next step would be intralesional triamcinolone 10 mg/mL injected directly into the nodule until it blanches slightly. Injections should be repeated every 3 to 4 weeks for a total of 2 to 3 injections.
The patient in this case had negative Lyme serology and was treated with 2 injections of triamcinolone 10 mg/mL administered 3 weeks apart. She experienced complete resolution.
Photos and text for Photo Rounds Friday courtesy of Jonathan Karnes, MD (copyright retained). Dr. Karnes is the medical director of MDFMR Dermatology Services, Augusta, ME.