Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.
A 40-year-old man is evaluated for a firm, flesh-colored lesion that has been growing on the back for several months. Foul-smelling material can be expressed from the lesion. The patient is bothered by the periodic drainage. He is otherwise healthy and takes no medications.
On physical examination, vital signs are normal. There is a 3-cm subepidermal nodule with a central punctum on the upper back. There is no erythema or warmth of surrounding skin.
Which of the following is the most appropriate treatment for this patient?
A. Excision
B. Incision
C. Incision and drainage
D. Oral antibiotics
MKSAP Answer and Critique
The correct answer is A. Excision.
This patient has an epidermal inclusion cyst (sometimes called epidermoid cyst), and the most appropriate treatment is excision. The diagnosis of epidermal inclusion cysts is clinical. Epidermal inclusion cysts range from a few millimeters to several centimeters in size and are subepidermal, freely movable nodules with an epithelial lining and a core of accumulated keratin debris. They are most commonly found on the trunk. Epidermal inclusion cysts are often incorrectly referred to as “sebaceous cysts,” a term that is erroneous because they possess keratin rather than sebum. Often they have a central punctum by which foul-smelling material can be expressed; the odor is derived from the presence of anaerobic bacteria. Epidermal inclusion cysts are benign but are frequently removed if they become bothersome to the patient. In this case, treatment is by excision with removal of the entire cyst wall.
When epidermal inclusion cysts rupture, they may become tender, inflamed, and occasionally infected. Ruptured cysts are often mistaken for furuncles or infectious abscesses. Ruptured cysts are treated with incision and drainage, and intralesional glucocorticoid injections may be used to reduce the inflammation.
Incision, as well as incision with drainage, can lead to temporary improvement of an inflamed epidermal cyst; however, recurrences are common as the epithelial lining must be removed for complete treatment. Therefore, these are not the preferred treatment.
Antibiotics are rarely required; they should only be used when there is concern for secondary infection.
Key point
- Excision is the most appropriate treatment for bothersome epidermal inclusion cysts since the epithelial lining must be removed for complete treatment.
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