Clinical features:
(1) more common in the proximal muscles of the lower extremities but can affect the upper extremities and distal limb muscles. It may also affect other sites such as extraocular muscles.
(2) muscles are swollen and tender
(3) muscular hypertrophy may be bilateral and symmetrical
(4) variable muscle weakness
Laboratory findings:
(1) elevated acute phase reactants (ESR, CRP)
(2) elevated angiotensin-converting enzyme activity
(3) variable serum concentrations of muscle enzymes, often normal
The chest X-ray may be negative for hilar lymphadenopathy.
Imaging studies may show the "three stripes" sign associated with fibrosis.
MRI is nonspecific but can be helpful to identify a muscle biopsy site. The MRI may show one of the following:
(1) muscle atrophy with fatty degeneration
(2) high T2 signal intensity
(3) a nodular pattern
(4) normal
Histologic findings on muscle biopsy:
(1) noncaseating granulomas
The diagnosis requires exclusion of other causes of granulomatous disease.
