Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 66-year-old man is evaluated for a persistent rash for 6 years’ duration. The rash waxes and wanes in severity, and it becomes pruritic only after he becomes hot and sweating, such as when he mows the lawn or exercises. It has always been limited to his back and lower chest. He has never treated it. The patient is otherwise well, has no other medical problems, and takes no medication.

On physical examination, vital signs are normal. There are small 2- to 3-mm red papules, some with slight scale, on his back and across the lower part of his chest. There are no lesions on his arms, legs, face, soles, or palms. The remainder of the examination is unremarkable.

Which of the following is the most likely diagnosis?

A: Bacterial folliculitis
B: Grover disease
C: Miliaria
D: Pityriasis rosea
E: Tinea versicolor

MKSAP Answer and Critique

The correct answer is B: Grover disease.

The most likely diagnosis is Grover disease (acantholytic dermatosis). Grover disease was initially described as a transient rash, but the clinical course can be quite variable; it may be self-limited, waxing and waning, or chronic and persistent. In most patients, it is characterized by red papules on the chest, flanks, and back. Some papules may be topped by a fragile vesicle or fine scale. It most often affects patients 50 years of age and older. Pruritus is exacerbated by heat and sweating; however, it may also be absent or minimal. A biopsy is usually not necessary but will show acantholysis characterized by dissociation of keratinocytes in the epidermis. Treatment includes reassurance, cooling measures, and low- to mid-potency topical corticosteroids, but regardless of treatment, it tends to be recurrent.

Bacterial folliculitis can affect the trunk, but also favors the beard, axillae, pubic area, buttocks, and legs. Patients often have pustules centered on hair follicles. Lesions may be painful, pruritic, or both. Infections are self-limited and do not persist for 6 years.

Miliaria rubra consists of red papules without scales on patches of skin that are occluded and hot, such as in neonates and hospitalized patients. The eruption can be asymptomatic, pruritic, burning, or stinging. The condition is self-limited and would not persist for 6 years.

Pityriasis rosea most commonly occurs during the spring or fall and classically begins with a single, pink, 2- to 4-cm, thin, oval-shaped plaque with a thin collarette of scale at the periphery (herald patch). Similar but smaller plaques subsequently erupt within days to weeks, usually on the torso along skin cleavage lines. Lesions can be asymptomatic or mildly itchy. The eruption usually lasts 4 to 10 weeks but may persist for months.

Tinea versicolor is characterized by slightly scaly hyper- or hypopigmented macules of the trunk and upper arms. The causative yeast organism, Malassezia furfur, often becomes clinically manifest when hot and humid environmental conditions favor its growth. Tinea versicolor is not papular and does not typically itch.

Key Point

• Grover disease is characterized by red papules on the chest, flanks, and back that may become pruritic with heat and sweating.

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