Bilateral accessory iliac horns: pathognomonic findings in Nail-patella syndrome. Scintigraphic evidence on bone scan.

Nail-patella syndrome is a rare hereditary (autosomal dominant) disorder, also called hereditary osteo-onychodysplasia and Fong's syndrome. Its incidence is 4.5 per million population in the United States. Patients have a characteristic tetrad of pathologic symptoms including fingernail dysplasia, hypoplastic or absent patellas, radial head dislocation, and iliac horns. Soft-tissue changes and renal dysplasia have also been associated with the syndrome. Iliac horns are bilateral accessory outgrowths consisting of cortex and medulla continuous with the iliac bone. They are located at the site of attachment of the gluteus medius muscles and project posterolaterally. These smooth bony outgrowths are asymptomatic, frequently palpable, and, because they have no effect on gait, they need not be treated. Iliac horns are the pathognomonic feature of Nail-patella syndrome; that is, they occur in approximately 80% of cases and are observed only in this condition. Four patients (two female, two male) with Nail-patella syndrome have been examined in the authors' department: three family members, including a 37-year-old woman, her 18-year-old son, and her 15-year-old daughter, and an unrelated 26-year-old man. All patients, regardless of age or sex, had similar pelvic findings on their bone scans. Although whole-body scans were obtained in all patients, significant scintigraphic findings were observed only in the pelvis in all the patients examined. This is most likely the result of the mild nature of the related deformities, which do not yield scintigraphically detectable osteoblastic changes. A representative image showing these independent ossification on a Tc-99m MDP bone scan is presented. A conventional pelvic radiographic image of the same patient's pelvis is presented for comparison.