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Recognizing and managing the musculoskeletal manifestations of sarcoidosis: the protean clinical manifestations can masquerade as other disorders.

Article Excerpt
Originally described by Boeck in the 1870s, sarcoidosis, or "new flesh formation," refers to the histological hallmark of the disease, noncaseating epithelioid granuloma. The noncaseating granuloma of sarcoidosis is a lesion composed of epithelioid cells that surround a central granular zone in a circular or arc pattern without necrosis. (1) The respiratory system is thought to be involved at some point in the lifetime of all patients with sarcoidosis (Figure 1). (2) However, the protean clinical manifestations (Table) can masquerade as a number of other disorders, because multiple organs--including the muscles, bones, and joints--can be affected.

Although musculoskeletal manifestations of sarcoidosis usually are not the presenting clinical feature, they are not rare. When looked for, they may provide clues to sarcoidosis when it presents in other tissues. Corticosteroids remain the most effective therapeutic intervention, but given the toxicity associated with their long-term use, management of sarcoid arthropathy, myopathy, and osseous lesions is best guided by the extent to which these manifestations are symptomatic. In this article, we describe our approach to recognizing and managing the musculoskeletal manifestations of sarcoidosis.

CAUSES AND EPIDEMIOLOGY

The etiology of sarcoidosis remains unknown. Men and women of all ages may be affected, but primarily young adults between the second and fifth decades are affected; there is a slight predominance in women. A second peak has been described in women older than 50 years. (3,4)

Epidemiological data have demonstrated ethnic and regional variations in the clinical presentations, disease course, and genetic susceptibilities of sarcoidosis; the incidence is higher in African Americans and Northern Europeans. (5) Familial aggregation and genomewide association studies have confirmed the genetic susceptibility.

The disease therefore is thought to be induced by environmental factors in genetically susceptible persons.

Airborne particulate, viral, or mycobacterial pathogens and occupational exposures have been postulated as potential triggers in the pathogenesis of the disease. The inflammatory response is a cell-mediated aggregation of [CD4.sup.+] [T.sub.H]1 phenotype lymphocytes with enhanced production of interleukin-12 and interferon-[gamma] within the granulomatous lesions. The otherwise suppressed immunity reflected in the fascinating anergy phenomenon to tuberculin testing is speculated to occur as a consequence of enhanced activity of circulating [CD8.sup.+] suppressor T lymphocytes and enhanced [T.sub.H]2 responses. However, the exact immunopathogenetic process that culminates in the clinical presentation of sarcoidosis remains elusive. (6)

Sarcoidosis may involve any organ system, manifesting a wide spectrum of disease severity. Extrapulmonary manifestations are common; they occur in the context of pulmonary features, except in a small minority of patients. Most notably, among patients with neurological involvement, it is important to recognize that the neurological lesions may be the presenting manifestation.

Extrapulmonary features, including musculoskeletal involvement, vary by gender and ethnic origin; the prevalence is higher among women and African Americans.

Although reports of the rate of musculoskeletal involvement vary, up to 40% of patients with sarcoidosis have documented musculoskeletal findings. (1-9) Musculoskeletal system involvement may be asymptomatic. This is important for clinicians looking for signs of sarcoidosis when considering it in the differential diagnosis of disease involving the eyes, CNS, or visceral organs. (5)

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