Seven cases in which osseous lesions of mastocytosis resemble metastatic malignant lesions in bone have been reported.

Mast cells, a normal connective-tissue element with complex physiopharmacological aspects, may proliferate abnormally and produce an unusual clinical syndrome: mastocytosis. The skin is usually the first and often the only organ involved. The resultant rash (urticaria pigmentosa) has a somewhat varied appearance but characteristically urticates or flushes with trauma.

In a small percentage of patients, the disease affects other organs, particularly the liver, spleen, and skeleton. The skeletal manifestations are often confused roentgenographically with those of metastatic carcinoma, as is manifested by the sequence of events in four of the seven cases reported here. Extensive osseous mastocytosis most closely resembles the myelosclerosis of agnogenic myeloid metaplasia. Typically, the differential roentgenographic features of osseous mastocytosis are the following:

1. The predominantly epiphyseal location in the long bones if scattered discrete lesions are present;

2. The sclerotic halo enveloping discrete lytic foci;

3. The uniform but non-homogeneous medullary distribution if extensive osteosclerosis is present;

4. The slight to moderate hepatosplenomegaly.

In most instances, the suspicion of the presence of osseous mastocytosis can be quickly substantiated by checking the patient's skin. Additional confirmation by bone biopsy is desirable although the number of mast cells in a given specimen may not be increased. Final diagnosis depends on correlation of the cutaneous, clinical, roentgenographic, and pathological findings.

Treatment is directed primarily at controlling symptoms produced by the elaboration of histamine by the abundant mast cells and at the secondary complications of systemic mastocytosis. Prognosis depends on the organs involved and the extent of the disease.