At the risk of cluttering the board with an overly technical explanation, here’s a cut and paste from a “Derm 101” site that will, unfortunately, sunset tomorrow. My apologies if it’s not useful. The key is distinguishing it from other conditions.

GROVER'S DISEASE

Grover's disease, named originally “transient acantholytic dermatosis” by Ralph Wier Grover, occurs in men and women who, almost always, are over 40 years of age and usually are over 60. The condition consists of papules that tend to erupt on regions exposed routinely to sunlight, especially the V of the chest and the upper extremities. Although the disease itself sometimes is transient, at other times it is persistent, not lasting for weeks but for years. The papules are of two types, one with a smooth surface and the other with a rough one as a consequence of its being keratotic.

The denominator in common for diagnosis histopathologic of Grover's disease is acantholytic dyskeratotic cells in one or more epidermal loci, a pattern designated “focal acantholytic dyskeratosis.” Without acantholytic dyskeratotic cells, a diagnosis of Grover's disease cannot be made. Four variations in arrangements histopathologic of acantholytic dyskeratotic cells are responsible for Grover's disease bearing a resemblance to Darier's disease, Hailey-Hailey disease, superficial pemphigus (pemphigus foliaceus), and deep pemphigus (pemphigus vulgaris). One particular combination of findings in the epidermis is unique to Grover's disease, namely, spongiosis in conjunction with focal acantholytic dyskeratosis; it is not found in the purely Darier, Hailey-Hailey, or pemphigus variants of Grover's disease.

Sections from a biopsy specimen of the Darier type of Grover's disease may be indistinguishable from those of authentic Darier's disease, consisting as they do of superficial perivascular infiltrates of lymphocytes above which are loci of suprabasal clefts atop which acantholytic, dyskeratotic cells punctuate the spinous and granular zones. Some parakeratotic cells at the summit of those loci also may be acantholytic. The only clues to differentiation of the Darier type of Grover's disease from true Darier's disease is the presence, as a rule, of more loci of acantholytic dyskeratotic cells per unit area of tissue and the propensity for eosinophils to appear in the upper part of the dermis. Neither of those findings, however, is seen consistently in Grover's disease. Sometimes Darier's disease, unlike Grover's disease, is unaffiliated with any infiltrate of inflammatory cells. Clinically, lesions of the Darier type of Grover's disease with their parakeratotic surface, just like those in Darier's disease, are perceived on palpation to be rough.

The Hailey-Hailey type of Grover's disease is characterized by loci of acantholytic dyskeratotic cells that extend throughout most of the thickness of the epidermis. Despite several findings in common between true Hailey-Hailey disease and the Hailey-Hailey type of Grover's disease, the latter usually can be distinguished from the former by the distinctly focal nature of it. Except for the very earliest stage in the evolution of Hailey-Hailey disease, acantholytic dyskeratotic changes tend to be confluent, not focal as in Grover's disease. The pemphigus vulgaris type of Grover's disease, like pemphigus vulgaris itself, displays suprabasal clefts and acantholytic cells, and no prominent parakeratosis. Unlike authentic pemphigus vulgaris, however, the pemphigus vulgaris variant of Grover's disease contains some acantholytic cells that are dyskeratotic. The superficial pemphigus type of Grover's disease is typified by a split in the granular zone with acantholytic dyskeratotic cells present slightly above and below the zone of separation. That variant of Grover's disease also differs from true pemphigus foliaceus by the focal nature of the process. Clinically, the papules in the Hailey-Hailey and pemphigus types of Grover's disease are smooth.

One type of Grover's disease is typified not only by acantholytic dyskeratotic cells in foci, but by spongiosis in close proximity. In none of the other four variants of Grover's disease is spongiosis a feature, nor is spongiosis a component of true Darier's disease. Therefore, when a histopathologist sees spongiosis in association with foci of acantholytic dyskeratotic cells, the diagnosis almost certainly is Grover's disease. If, in addition, there are numerous eosinophils in the infiltrate, a diagnosis of Grover's disease is confirmed. Parenthetically, the more eosinophils present in the dermis of Grover's disease, the more maddening is the pruritus associated with it and the more refractory the condition is to therapy.

In conclusion, a variety of clues enable Grover's disease to be differentiated from diseases that simulate it histopathologically, those being Darier's disease, Hailey-Hailey disease, pemphigus vulgaris, and pemphigus foliaceus. Among those clues are spongiosis, serum, crusts, and evidence of excoriation. Any of them alone, particularly spongiosis, in conjunction with changes of focal acantholytic dyskeratosis signifies Grover's disease.