Case report: MR features of granulomatous myositis

Abstract

A 51-year-old woman with a 23-year history of systemic lupus erythematosus (SLE), on long-term low-dose steroids, presented with right thigh swelling and erythema of 2-weeks duration. She was afebrile and denied antecedent trauma or injection. Relevant past history included right caphalic vein thrombosis; and culture and biopsy proven cutaneous tuberculous granulomas of the right forearm 3 years ago, which responded to a 9-month regimen of rifampicin, isoniazid and ethambutol. The WBC count was 13.8 x 109/1 with granulocytosis (92%) and lymphopenia (690//zl). Serum creatinine phosphokinase (1211 u/l) and aldolase (32.4u/1) levels were elevated. Doppler study of the right lower limb excluded a deep vein thrombosis. Magnetic resonance (1.5 T) images showed subcutaneous oedema and abnormal signal intensity in the quadriceps femoris. On Tl-weighted (SE 600/17) images, the swollen muscles were slightly hyperintense to normal muscle with loss of inter-muscular planes (Figs la & 2a). These areas enhanced moderately following intravenous gadolinium-DTPA and were hyperintense on the T2-weighted (FSE 4000/102) images (Figs lb & 2b). Fast multiplanar inversion recovery (FMPIR 3000/102) (Fig. 2c) accentuated the abnormalities. These signal and enhancement characteristics suggested myositis. No bony abnormality was detected. Open muscle biopsy of the abnormal rectus femoris and vastus intermedialis muscles revealed granulomatous myositis, with extensive myocyte necrosis surrounded by epitheloid histiocytes, multinucleated giant cells and lymphocytes. There was no evidence of acid fast bacilli (AFB), fungus or vasculitis. The tissue and blood cultures were also sterile. The patient did not receive specific therapy for her thigh swelling and was discharged. Shortly after, dusky erythematous plaques and nodules in a sporotrichoid distribution erupted predominantly in the swollen right lower limb. The dermatologist's clinical diagnosis was an atypical mycobacterial skin infection. Skin biopsy showed granulomas with caseous necrosis and AFB, but cultures for mycobacteria were negative. Very rapid clinical response to empirical treatment with clarithromycin and ciprofloxacin for atypical mycobacterial infection ensued. After 3 months, treatrnent was ceased for suspected antibiotic-induced purpura (subsequently found to be caused by NSAIDs). Within 2 weeks, the lesions relapsed. Repeat skin biopsies all confirmed cutaneous tuberculous infection. Multiple cultures for mycobacteria from skin specimens, sputum and laryngeal swabs were negative. The chest radiograph was normal and MRI of the himbosacral spine excluded vertebral osteomyelitis. Resumption of the antibiotics, reinforced with ethambutol, isoniazid and rifampicin, finally saw gradual resolution of the right thigh swelling and skin lesions., On the follow-up MR imaging, 8 months from commencement of therapy, there was significant resolution of the abnormal signals in the right thigh (Fig. 3). literature search (Medline: 1976-March 1995), but none of atypical mycobacterial myositis. Our patient was proven on multiple skin biopsies to have cutaneous mycobacterial infection, and the clinical picture was that of atypical mycobacteria. The granulomatous myositis diagnosed on biopsy 1 month before the onset of the cutaneous lesions was also mycobacterial in origin, as there was resolution, clinically and on repeat MRI, following anti-tuberculous therapy. Pyogenic myositis, caused by Staphylococcus aureus in more than 90% of cases [5], is endemic in the tropics where it accounts for 4% of surgical admissions [6]. It occurs infrequently in the temperate climates, but has been increasingly reported in North America and Europe. It affects all ages, and typically involves a single large muscle group, usually the thigh (quadriceps femoris), although multiple muscle involvement is found in 12% to 43% [7]. It is associated with trauma (in 20% to 50% of cases), a history of travel to the tropics, nutritional deficiencies, underlying parasitic or occult viral myositis, and immunocompromised states. These include diabetes mellitus, infection with human immunodeficiency virus, leucopenia with leukaemia, Felty's syndrome, rheumatoid arthritis, and progressive systemic sclerosis [8]. We are unaware of any case previously reported in an SLE patient. Corticosteroid therapy