Osteomyelitis Variolosa, A Differential Diagnosis of a Multifaceted Condition
Recently, we read with great interest the clinical case and x-ray description of osteomyelitis variolosa by Thomas1 in the Journal of Clinical Rheumatology. The case impresses for bilateral shortening of several metacarpals and phalangeal bones. Late skeletal manifestations of smallpox can be recognized years after the original infection, in the form of shortening of tubular bones, flail joints, subluxations, dislocations, gross bony deformities, premature osteoarthritis, and joint ankyloses.2
We would like to comment on the differential diagnosis of short bones (brachydactyly) as found in the case of osteomyelitis variolosa reported by Thomas, which may be an isolated finding or also be part of a more complex syndromic form. Brachydactyly is a general term that refers to disproportionately short fingers and toes and forms part of the group of limb malformations characterized by bone dysostosis.3,4
The clinical spectrum of brachydactyly can widely range from minor digital hypoplasia to complete aplasia. Single or multiple bones of individual digits, single bones of multiple digits, or multiple bones of different digits may be involved.5 Isolated forms usually show an autosomal dominant pattern of inheritance with variable expression and penetrance, although there are a number of syndromic forms of brachydactyly associated with various anomalies including diverse skeletal and joint malformations, cardiac conduction defects, nephritis, mental retardation, and sensorineural deafness.3
Differential diagnosis of osteomyelitis variolosa presenting with shortening of long bones and flared metaphysis may give a superficial resemblance to achondroplasia. In the cases of bone sequelae of small pox, there is no true symmetry of bone involvement. In consequence, there is often inequality in bone length.6 Shortening of the tubular bones of the hands and feet seen in some cases of small pox should not be mistaken for pseudo-pseudo-hypoparathyroidism,2 a syndrome with a wide range of manifestations including short stature, obesity, subcutaneous ossifications, and brachydactyly mostly affecting the fourth and fifth rays.
Many other conditions may have similar presentations to osteomyelitis variolosa, such as sequelae of septic arthritis,7 burns, congenital dysplasia,8 and leprosy. Cases of osteomyelitis variolosa presenting with the typical tapered, “licked candy stick” appearance have been reported.7 Caffey disease9 or infantile cortical hyperostosis may be considered in the differential diagnosis, it often affects the mandible, clavicle, ribs, and scapula, distribution that is different from osteomyelitis variolosa. A description of a case of osteomyelitis variolosa misdiagnosed as rheumatoid arthritis because of bilateral and symmetric joint involvement, fixed flexion deformities, and positive rheumatoid factor was also reported.10
A detailed history and clinical and radiological examination including extensive differential diagnoses are necessary to distinguish osteomyelitis variolosa11 from other similar pathologies and to arrive at a correct clinical diagnosis; even in this post–eradication era of smallpox, we might still find cases of its sequelae in countries where it was once endemic. Inquiry for a history of smallpox is suggested when unusual joint deformities and growth inequalities of the extremities are present.