[Acquired cutaneous osteomatosis. A primary monomelic form]

Eight cases of sporadic acquired primary osteoma cutis have been reported in the literature. Age at onset varies from 16 to 55 years with a mean of about 35 years. The sex ratio is 1 and a wide range of localizations have been reported. There is no known treatment. We report a new case of primary osteoma cutis observed in an adult. The monomelic feature of this case has not been reported previously. The patient was 76 years old and had multiple painless, stone-like formations at several sites on the left thigh and leg since the age of 40. Histological examination of skin biopsies showed a perfectly differentiated bone tissue in the dermal layer. There was no similar family history nor abnormal morphotype. Likewise, the absence of laboratory signs of pseudohypoparathyroidism, together with the late and spontaneous onset allowed us to eliminate hereditary Albright's osteodystropy or secondary osteomatosis due to a local pathological process. Despite the late onset, the monomelic character of the osteomas observed and the association of hemicorporeal hypertrophy and linear basocellular naevi reported in the literature would suggest a hamartomatous origin rather than a metaplasic process in this patient.