Differentiating osteopoikilosis from osteoblastic metastases

ABSTRACT: Osteopoikilosis is a rare, benign osteosclerotic dysplasia that predominantly involves the appendicular skeleton. Radiographic findings are diagnostic, and the disease often is discovered incidentally on x-ray films. The importance of recognizing osteopoikilosis lies in differentiating it from osteoblastic metastases. The cause is unclear. Patients typically are asymptomatic. Diagnostic findings include the appearance of numerous small, well-defined, spheroid sclerotic foci. Because evidence suggests an association with skeletal and dermatological changes, evaluation for coexisting pathological conditions may be warranted. The differential diagnosis for a patient who has radiographic characteristics similar to those of osteopoikilosis includes osteoblastic metastases, mastocytosis, tuberous sclerosis, melorheostosis, and osteopathia striata. (J Musculoskel Med. 2008;25:387-389)

Osteopoikilosis, which literally means "spotted bones," is a rare, benign osteosclerotic dysplasia that was first described in the early 20th century.^1-5 The disease, seen in men and women of all ages, predominantly involves the appendicular skeleton. It occurs most often in bones of the hands and feet, although lesions are seen scattered around larger joints.^3,5,6 The pathogenesis is unknown, although mutations in the LEMD3 gene may be the cause.^7,8

Radiographic findings are diagnostic, and the disease often is discovered incidentally on x-ray films. Medical evaluation may be important, however, because there may be coexisting developmental or pathological conditions.⁹

The importance of recognizing osteopoikilosis lies in differentiating it from osteoblastic metastases.² Gaining a better understanding of the disease may alleviate both patient and physician anxiety. In addition, having knowledge of this radiographic entity may minimize unnecessary testing and medical costs. In this article, we describe the epidemiology of osteopoikilosis, the history and physical examination, radiographic characteristics, the histology, associations with skeletal and dermatological changes, and the differential diagnosis.

Incidence, epidemiology, causes
The incidence of osteopoikilosis is estimated at 1 in 50,000; the disease is seen in up to 6 per 100,000 radiographs.^3,10 This benign skeletal dysplasia has no age or sex predilection. Osteopoikilosis usually is discovered in patients aged 15 to 60 years, but fetal and geriatric cases have been reported. The cause of osteopoikilosis is unclear. The disease probably is transmitted in an autosomal dominant fashion, although sporadic forms are documented.^5,9,11-13 The pathogenesis is thought to involve perturbation of collagen(Drug information on collagen) regulation or failure to form trabeculae along the lines of stress.^5,10 Evidence suggests a relationship with other osteosclerotic skeletal disorders, especially osteopathia striata and melorheostosis.^4,13

History and physical examination
Patients with osteopoikilosis typically are asymptomatic, although 15% to 20% report mild articular pain and joint effusion.^5,11,14 Overt external physical findings otherwise are absent. Whether the mild symptoms are related to osteopoikilosis or to the inciting injury that led to the indication for radiography is uncertain.^5,9,11 Because the condition is thought to be without symptoms, discovery by radiographic examination most often is incidental.

Radiographic characteristics
Findings diagnostic of osteopoikilosis include the appearance of numerous small, well-defined, spheroid sclerotic foci—usually ranging from 2 to 10 mm—clustered in periarticular regions (Figure).^3,5,9 These well-delineated opacities most often are seen in the small bones of the hands (carpus) and feet (tarsus).⁵

Figure – Radiographic findings diagnostic of osteopoikilosis include the appearance of numerous small, well-defined, spheroid sclerotic foci clustered in periarticular regions in the shoulder (A), ankle (B), and pelvis (C).