Abstract

Pseudobullous pilomatricoma is a rare variant of pilomatricoma, a benign skin tumor that originates from the hair matrix. The incidence of bullous or pseudobullous pilomatricoma is not well established due to its rarity, however, it has been reported in children with a female predominance. A pilomatricoma typically presents clinically as a firm, solitary nodule and is histopathologically characterized by basaloid cells that keratinize to form ghost cells, and commonly calcifications with multinucleated giant cells.

Here, we report a case of an 18-year-old female who presented with a six-month history of a progressively worsening tender nodule on her back. Clinical examination was notable for a well demarcated elliptically shaped bulla measuring 3.0 x 4.0 cm with a firm, tender, and mobile nodule centrally. Imaging demonstrated a well circumscribed 13 mm soft tissue nodule in the subcutaneous fat. A punch biopsy of the nodular component of this lesion was consistent with pilomatricoma. The lesion was later excised in its entirety with pathology showing irregular bundles of collagen with increased fibroblasts and capillaries consistent with scar. No dilated lymphatics were observed. The presentation of this pilomatricoma as a bullous lesion is an unusual finding, as pilomatricomas typically present as firm nodules. Hypotheses for the bullous presentation include the production of elastinolytic enzymes by the tumor affecting the elastic fibers leading to destruction and dilation of lymphatics, growth of the tumor compressing the lymphatics leading to congestion of fluid and subsequent dilation of lymphatics, and mechanical irritation of the tumor itself.