Histiocytoid neutrophilic dermatoses and panniculitides: variations on a theme.

Requena et al, in their article titled "Histiocytoid Sweet syndrome," in 2005, established that the dermal infiltrate in some patients with Sweet's syndrome is composed of histiocyte-like immature myeloid cells, not polymorphonuclear leukocytes as is the norm. With this premise in mind, we report on 6 cases of inflammatory skin disease in which the common denominator was a dermal and/or subcutaneous infiltrate of histiocytoid myeloid cells in patients with new-onset cutaneous eruptions and systemic symptoms. The cases were diverse clinically and microscopically, fell short of the criteria necessary for a diagnosis of classical Sweet's syndrome, and were difficult to categorize at the outset. The systemic manifestations ranged from malaise alone to a combination of fever, chills, night sweats, and polyarthralgia. The clinical morphology of the cutaneous eruptions varied from being papulovesicular in 1 patient to mainly consisting of erythematous plaques and nodules in the remainder. The dermatologists' differential diagnoses included Sweet's syndrome in 3 cases, a drug eruption in 2, and other entities such as erythema nodosum and Well's syndrome. Biopsies in all cases revealed a dermal and/or subcutaneous infiltrate composed predominantly of mononuclear histiocytoid cells of myeloid origin. With the benefit of detailed clinicopathologic correlation, the cases were classified for the purpose of this report as follows: Sweet's-like neutrophilic dermatosis, histiocytoid (3 cases); subcutaneous Sweet's syndrome, histiocytoid (2 cases); histiocytoid neutrophilic dermatosis, unspecified (1 case). In addition, we describe a further instructive case that exhibited overlap with those in the series but proved ultimately to represent leukemia cutis. The spectrum of observations in this report supports and expands the original concept of histiocytoid Sweet's syndrome.