ANSWER
The correct answer is Grover disease (choice “c”).
DISCUSSION
Grover disease—also known as transient acantholytic dermatosis—was first described in 1975 by Ralph Grover, MD, and is now recognized as a relatively common condition, especially in White men older than 40. Its appearance on darker skin is unusual. The morphologic presentation seen in this case is fairly typical, though most patients complain more about itching than this patient did.
The actual cause of Grover disease is unknown. Heat, sweat, and sunlight are suspected triggers. Its appearance can be associated with certain medications, recent treatment with ionizing radiation, or end-stage renal failure.
Biopsy is the key to diagnosis of Grover disease, especially in the context of the clinical presentation. This method also serves to rule out the other items in the differential.
Tinea corporis (choice “a”) was ruled out by the KOH as well as the rash’s appearance. Darier disease (choice “b”)—otherwise known as keratosis follicularis—is an inherited dermatosis that presents with multiple findings on skin, nails, and mucous membranes; however, the papulosquamous rash would be far more coarse than what manifests in Grover disease, and it would have manifested at a much earlier age. While folliculitis (choice “d”) was a possibility in this patient, the biopsy ruled it out.
TREATMENT
Grover disease is notoriously difficult to treat. Although it is described as a “transient” dermatosis, it can last months to years despite all therapeutic efforts.
This patient was treated with a stronger topical steroid (0.05% betamethasone cream) twice a day and minocycline (100 mg/d) for 2 months. These cleared his rash.