SAEM Clinical Images Series: Back Lesion

skin lesion

An 18-year-old-female with no known past medical history presented with a lesion on her back that had been present and enlarging for five months. It was not painful unless she touched it, and then only mildly tender. She denied any known cause, wound, prior rash, or other lesions. Her review of systems and past medical history were negative.

Additional Images

Physical Exam

Vitals: Normal

Skin: An erythematous lenticular, or biconvex, lesion with distinct borders is noted at the left posterior thorax below the scapula. It is soft with some slight nodularity on palpation, and only mild tenderness noted. There is no fluctuance. No other skin lesions are present. The rest of the examination is normal.

Laboratory Data

Ultrasound reveals a 1.7 x 0.8 x 1.1 cm superficial soft tissue mass inferior to the scapula on the left thorax.

CT scan of the chest confirms no intrathoracic extension or other lesions.

Case Question: Is the next appropriate step antibiotics, antifungals, topical steroids, or biopsy?

Biopsy is the next appropriate step. The lesion does not appear to be infectious, either viral, bacterial, or fungal. Furthermore, it has no appearance of an inflammatory reaction that would benefit from topical steroids. The differential includes a cystic structure, neurofibroma, or malignancy. Because of the concern for malignancy, a biopsy was performed in the emergency department after the ultrasound and CT scan confirmed there was no extension into the thorax. The biopsy revealed a pilomatrixoma, or pilomatricoma. Pilomatrixoma is a superficial benign skin tumor that arises from hair follicle matrix cells. They commonly occur in the first two decades of life with a mean age of 17 years. The most common presentation is an asymptomatic, firm, slowly growing mobile nodule. However, only 16% are accurately diagnosed on clinical examination. This case reveals the wide variation in visual presentation and confirms the inability to diagnose the lesion at the bedside. Complete surgical excision is curative.

Case Discussion

Take-Home Points

Unknown skin lesions, with concern for malignancy, should be diagnosed by biopsy.
Pilomatrixoma is rarely diagnosed at the bedside.

References

Jones CD, Ho W, Robertson BF, Gunn E, Morley S. Pilomatrixoma: A Comprehensive Review of the Literature. Am J Dermatopathol. 2018 Sep;40(9):631-641. doi: 10.1097/DAD.0000000000001118. PMID: 30119102.

Copyright

Images and cases from the Society of Academic Emergency Medicine (SAEM) Clinical Images Exhibit at the 2023 SAEM Annual Meeting | Copyrighted by SAEM 2023 – all rights reserved. View other cases from this Clinical Image Series on ALiEM.