Summary The clinical features of eight cases of multicentric reticulohistiocytosis are presented. Although minor variations do occur, the disease is generally a well delineated and homogenous entity. Treatment is discussed briefly but, with the possible exception of cyclophosphamide, has proved relatively ineffective. Emphasis is given to the relationship between multicentric reticulohistiocytosis and malignant disease, which has now been reported in eighteen of seventy‐four cases.

Two infants experienced subcutaneous fat necrosis (SCFN) at a relatively late age after cardiac surgery with induced hypothermia. The condition resolved in both patients over four weeks without treatment. The appearance of SCFN after the newborn period is very unusual, and in these patients was probably related to the hypothermia.

Pityrosporum orbiculare is an obligate lipophilic yeast in vitro, which suggests it possesses an extracellular lipase crucial for nutrition. If present in vivo, the enzyme would enable the yeast to utilize skin surface lipids, which may therfore play an important role in the pathogenesis of pityriasis versicolor. Cultured P. orbiculare and biopsy material from patients with pityriasis versicolor were investigated for the presence of lipase by electron microscope histochemistry. At sites of lipase activity, fatty acid hydrolyzed from Tween 80 substrate reacts with Ca++ ions to form an insoluble Ca++ soap. Exchange of Ca++ with Pb++ enables the sites of lipase activity to be visualized as electron dense deposits of insoluble lead soap. Surface lipase activity was apparent when the technique was applied to P. orbiculare grown on lipid containing medium and its specificity confirmed by removal of substrate and inhibition by di-isopropyl fluorophosphate and quinine hydrochloride, but not by sodium fluoride. When the same technique was applied to stratum corneum infected with Pityrosporum furfur (Malassez), no reaction product could be detected. It is postulated that lipase, although critical for fungal nutrition in vitro, is unlikely to be of importance in vivo. Skin surface lipids are therefore probably not relevant to the pathogenesis of pityriasis versicolor.

Multicentric reticulohistiocytosis developed in a 45-year-old woman, who had a 3 year history of untreated breast carcinoma. A review of the literature revealed that malignant disease has been associated with 27% of reported cases. It is considered that, like adult dermatomyositis, the onset of multicentric reticulohistiocytosis should stimulate detailed investigation for an underlying neoplasm.