A 35-year-old man comes to the office due to a 2-month history of a skin bump on his lower back. He noticed a similar bump in the same location 6 months ago, which spontaneously resolved after 3 weeks. The patient recalls no trauma preceding either occurrence. The bump has grown slightly larger in the past month, but there is no associated pruritus, pain, or other symptoms. His medical history is unremarkable, and he has no history of tobacco or alcohol use. Vital signs are within normal limits. Skin examination shows a firm, mobile nodule, as shown in the image below. There is no drainage from the lesion or tenderness to palpation. The lesion does not change shape when pinched at the edges. The remainder of the physical examination is within normal limits. Which of the following is the most likely diagnosis?

Question

A 35-year-old man comes to the office due to a 2-month history of a skin bump on his lower back.  He noticed a similar bump in the same location 6 months ago, which spontaneously resolved after 3 weeks.  The patient recalls no trauma preceding either occurrence.  The bump has grown slightly larger in the past month, but there is no associated pruritus, pain, or other symptoms.  His medical history is unremarkable, and he has no history of tobacco or alcohol use.  Vital signs are within normal limits.  Skin examination shows a firm, mobile nodule, as shown in the image below.  There is no drainage from the lesion or tenderness to palpation.  The lesion does not change shape when pinched at the edges.  The remainder of the physical examination is within normal limits.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

This patient has an epidermal inclusion cyst (EIC), also known as an epidermal cyst, a discrete benign nodule lined with squamous epithelium that contains a semisolid core of keratin and lipid. An EIC occurs when the epidermis becomes lodged in the dermis due to trauma or comedones, or it can arise de novo. EICs can be seen anywhere on the body, but are most common on the face, neck, scalp, or trunk. The lesion can gradually increase in size and may intermittently produce a cheesy white discharge. Some patients may develop significant inflammation with rupture and involvement of surrounding tissue. An EIC will usually resolve spontaneously but can recur. Diagnosis is made clinically with examination showing a dome-shaped, firm, and freely movable cyst or nodule with a central punctum (small, dilated, pore-like opening). Excision is typically performed only for cosmetic reasons. Incision and drainage are occasionally needed for infected and fluctuant cysts that are painful and erythematous. punctum (Choices A and E) Basal cell carcinoma is the most common type of skin cancer and usually presents as a pearly papule or plaque with small telangiectasias on sun-exposed areas. Squamous cell carcinoma is the second most common skin cancer and also occurs primarily on sun-exposed areas. The lesions are usually firm and scaly papules, plaques, or nodules. Neither type of skin cancer will show a central punctum, and the skin overlying this patient's nodule shows no signs of malignancy. Basal cell carcinoma Squamous cell carcinoma (Choice B) Dermatofibroma is a benign fibroblast proliferation that typically appears as a firm, hyperpigmented nodule, most often on the lower extremities. Dermatofibromas have a fibrous component that causes dimpling in the center when the area is pinched ("dimple" or "buttonhole" sign). Dermatofibroma (Choice D) Lipomas are benign, painless subcutaneous masses with normal overlying epidermis. In contrast to epidermal cysts, lipomas are usually soft to rubbery and irregular, and do not typically regress and recur. Lipomas Educational objective: Epidermal inclusion cyst is a benign nodule containing squamous epithelium that produces keratin. It presents as a dome-shaped, firm, freely movable cyst or nodule with a small central punctum. The lesion can remain stable or gradually increase in size but may produce a cheesy white discharge; it usually resolves spontaneously. References: Epidermal inclusion cyst embedded in a recurrent benign fibrous histiocytoma. (http://www.ncbi.nlm.nih.gov/pubmed/25284857)

A 35-Year-Old Man Comes to the Office Due to a 2-Month