en in individual bones is unpredictable. The femur is the most commonly and severely affected bone and hence most useful for radiographic screening of possible patients. Radiographs provide a meaningful assessment of disease activity and extent. The severity of symptoms is generally proportionate to severity of involvement shown by roentgenography. Exophthalmos due to osteosclerotic dysplasia of the skull occurred in more than half of the patients with progressive diaphyseal dysplasia. Twelve-year follow-up of this family, with affected individuals ranging in age from 6 months to 12 years, indicates that progressive diaphyseal dysplasia may progress or become quiescent and be remarkably inactive despite advanced osteosclerosis and structural deformity.1f:T45d,The clinical and biochemical features of four adults with Engelmann's disease (Camurati-Engelmann disease; progressive diaphyseal dysplasia) are presented. One young patient, with a particularly severe form of the disease, is discussed in detail. Biochemical abnormalities were found in three of the patients. In two of them, one with localized hyperostosis and one with generalized bone disease, the only changes were an increase in the plasma alkaline phosphatase and urinary total hydroxyproline excretion. The most severely affected patient, who had had progressive and generalized bone disease from age two and a half years, also had persistent hypo-calcaemia and hyperphosphataemia, a positive calcium balance, and a very low urine calcium excretion. It is suggested that some patients with Engelmann's disease may have a previously unrecognized metabolic disorder associated with increased retention of calcium and excessive bone formation. The possible role of abnormal phosphate metabolism in this increased formation of bone, and the relationship of Engelmann's disease to other hyperostoses, are discussed.20:T482,Progressive diaphyseal dysplasia, since its original description by Engelmann in 1929,¹has been characterized by progressive osteosclerosis of the diaphyses of the long bones associated with neuromuscular abnormalities. An underdeveloped physical state with muscular weakness and a wide-based waddling gait has been a prominent and constant finding.^2,3Although muscle biopsies have been generally unrevealing,^4,5Singleton et al reported in 1956 the presence of atrophic muscle fibers with degenerative changes.⁶Central nervous system (CNS) findings have included varied tendon reflex responses, ankle clonus, optic atrophy, and nystagmus.^2,3,7,8Lennon, Schechter, and Hornabrook⁸in 1961 attributed some of these neurological changes to narrowed cranial nerve exit foramina of the skull. Additional skeletal abnormalities have included prominent and symptomatic lordosis, scoliosis, flat feet, and knock-kneed and bowlegged deformities.⁴ Roentgenograms of the long bones have revealed symmetrical diaphyseal sclerosis bilaterally with thickening of the periosteum and endosteum.

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