Pityriasis maculata et circinata; Herpes tonsurans maculosus
Definition. An acute, self-limited, inflammatory disease of the skin characterized by small papules which soon develop into slightly elevated, round macules of a pale rose color, covered with thin, adherent, branny or fine scales.
Symptoms. While mild constitutional disturbances may be present, the temperature seldom goes above 102* F. A few lesions may precede the general eruption by a week or more, but when the active attack ensues, the eruption comes out in the course of the or two weeks. The lesions may wary from a few to hundreds, and while the trunk and thighs are the favorite location, the arms and legs may be involved. They are pink or rose colored macules or papulomacules which increase peripherally, often reaching the size of a silver half dollar. Oval patches are not infrequent, their greatest length corresponding to the cutaneous lines of cleavage. Central involution often occurs, giving an annular or circinate appearance to the lesions, which then typically present a slightly reddened and elevated border, a yellowish-white or fawn-colored center covered with a slight scaling. A few patches may coalesce but it is more usual for them to remain distinct. The disease runs a course of from two weeks to three months, although there are instances of it having lasted even six months. The itching, if present at all, is apt to be very slight and only at night.
Etiology and Pathology. The former is obscure, neither age nor sex appearing to influence it, although my own observations point to secondary anemia as the main factor in no less than sixteen cases. The duration of the diseases and the few recurrences point to some toxic principle developed in the body, but there is a growing tendency to believe that a parasite is causative and that the diseases is contagious in a very slight degree. Unna and other investigators found that the pathological change in the early stage or in the mild cases was of the nature of a mild serous and hyperplastic inflammation in the upper cutis. In the later stages this process is more emphasized and minute vesicles, only visible microscopically, form beneath the horny layer as the disease reaches its acme, and the absence of phagocytes in these vesicles leads Sabouraud to infer that pityriasis rosea is not parasitic, but rather a vesicular erythema of toxic origin.
Diagnosis. This disease may resemble tinea circinata, psoriasis, syphilis, dermatitis seborrhoea and tinea versicolor.
Tinea circinata is more distinctly ring-shaped with a decided tendency to clear in the center even if the patches are small. It is rarely as scattered or profuse as pityriasis and its fungus can be found by the microscope.
Psoriasis does not show a preference for the same locations as pityriasis rosea; its round or circinate patches are more elevated, of a deeper red, and often show the congested or bleeding papillae on removal of its, larger, whiter and thicker scales.
The scaly maculopapular syphilid is darker colored, is distinctly infiltrated, and its lesions are not uncommonly seen on the palms and soles. There are usually other signs of syphilis present.
Dermatitis seborrhoea of a mild degree may resemble pityriasis rosea when it begins to fade and takes on a yellowish tinge, but the scales of seborrhoea are fatty, easily removed, the surface of the patches may become moist, or easily bleed if irritated by friction and it may last for months or years.
Tinea versicolor is never acute in its course, and its patches are yellowish- brown rather than rose-red in color. A microscopic examination of the scales will always show the presence of the microsporon furfur in tinea versicolor.