Uncommon Clinical Course of Multiple Osteochondromatosis in a Patient with a Long-Term History of Cushing's Disease

Cushing's disease (CD), the chronic endogenous hypercortisolism derived from an ACTH-secreting pituitary adenoma, and multiple osteochondromatosis (MO), a congenital mesoderm dyschondroplasia, represent two distinct rare neoplastic diseases. Clinical appearance of MO usually occurs during the first-second decade of life. In fact, the growth of osteochondromas parallels the patient's growth, then becoming quiescent after the closure of the epiphyses and the achievement of final stature. Here we describe an uncommon case of a patient with a long-term history of childhood-onset CD, who surprisingly developed MO during the third decade of life, after the remission of CD. Indeed, a female patient had been followed for CD from the age of 12 to the age of 24 years, when CD definitively remitted. At the age of 26 the patient complained progressively worsening backache and pain at level of hips and feet. Standard radiography of skeleton showed multiple bone dysmorphisms at level of the four limbs, spine and pelvis consistent with multiple osteochondromas and exostoses. A diagnosis of MO was performed. Total body bone scintigraphy with ^99mTc-MDP revealed an increased uptake of the radioligand, suggesting an increased metabolic turnover in correspondence of the majority of the osteochondromas. However, the negativity of the majority of the lesions at ^99mTc-DMSA scintigraphy and the histological diagnosis of benign osteochondroma of the only positive lesion at ^99mTc-DMSA evidenced that the high metabolic activity of the osteochondromas was not due to malignant transformation. However, the activity of the lesions was highly surprising considering that they usually become quiescent after the achievement of the final stature. In last analysis, the uncommon characteristics of MO and, particularly, its occurrence after stable remission of hypercortisolism, suggests a possible role of glucocorticoids in influencing the clinical course of the skeletal disease. The inhibitory effect of hypercortisolism on bone growth and maturation could explain the block in the proliferation of skeletal lesions during the developmental age, where CD was in the active phase, and the opposite effect of stimulation of the ostochondromas growth during stable normalization of cortisol secretion, after CD remission.