ESSENTIALS OF DIAGNOSIS
Firm dermal papule or nodule.
Overlying black comedone or “punctum.”
Expressible foul-smelling cheesy material.
May become red and drain, mimicking an abscess.
Epidermal inclusion cysts (EICs) are common, benign growths of the upper portion of the hair follicle. They are common in Gardner syndrome and may be the first sign of the condition.
EICs favor the face and trunk and may complicate nodulocystic acne vulgaris. Individual lesions range in size from 0.3 cm to several centimeters. An overlying pore or punctum is characteristic. Dermoscopy can aid in observing a tiny punctum when not visible to the naked eye. Lateral pressure may lead to extrusion of a foul-smelling, cheesy material.
EICs are distinguished from lipomas by being more superficial (in the dermis, not the subcutaneous fat) and by their overlying punctum. Many other benign and malignant tumors may superficially resemble EICs, but all lack the punctum.
EICs may rupture, creating an acute inflammatory nodule very similar to an abscess. Cultures of the expressed material will be sterile.
Treatment is not required if asymptomatic. Inflamed lesions may be treated with incision and drainage or intralesional triamcinolone acetomide 5–10 mg/mL. For large or symptomatic cysts, surgical excision is curative.
et al. Importance of keen observation for the diagnosis of epidermal cysts: dermoscopy can be a useful adjuvant tool. J Am Acad Dermatol. 2014 Oct;71(4):e138–40.