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Myalgia has a broad differential diagnosis (Box 1). Sometimes the patient's country of origin is relevant.
An Angolan man aged 23, resident in the UK for 7 years, developed a 'flu-like illness with dry cough, coryza, headache, fever and myalgia. Symptoms resolved but returned a few weeks later, this time with night sweats, weight loss, severe myalgia in the forearms, thighs and calves and difficulty walking due to pain and weakness. He was unable to climb stairs or walk more than 10 metres. He also complained of morning stiffness in his knees and ankles. His general practitioner prescribed oral cefalexin, amoxicillin and indomentacin with some improvement.
On referral he was afebrile. Painless lymph nodes were palpable in the right axilla. Muscle bulk was reduced in his arms and legs, and the biceps, forearm extensors, quadriceps and calves were tender to palpation. Power was normal in the upper limbs and MRC grade 3-4/5 in the lower limbs, though difficult to assess because of pain. Reflexes and sensation were normal.
Initial investigations showed a normocytic anaemia with haemoglobin 9.0g/dL (normal range 13.0-17.0), total white cell count 4.8 × 109/L (3.0-10.0), lymphocytes 0.6 × 109/L (1.5-4.0), platelets 303 × 109/L (150-400), erythrocyte sedimentation rate 93 mm/h (0-20) and C-reactive protein 138 mg/L (0-5); albumin was 30 g/L (35-50), alkaline phosphatase 154 U/L (45-122), alanine aminotransferase 109 U/L (7-63), creatine kinase 243 U/L (24-195). Further normal or negative investigations were: plasma urea, electrolytes and calcium; immunological investigations (antinuclear antibody, rheumatoid factor, extractable nuclear antigen); an infection screen (urine culture, blood cultures, urine/blood mycobacterial culture); viral serology (Epstein—Barr, cytomegalovirus, HTLV-1, HIV); X-ray and chest abdominal/pelvic ultra-sound; nerve conduction studies and electromyography.
A CT scan showed a mass in the right axilla, and at operation several large axillary lymph nodes were found. The biggest was excised and acid-fast bacilli were seen on smear staining. Caseating necrosis and epithelioid granulomata were seen on histological examination. Tuberculous lymphadenitis was diagnoses and the patient was started on rifampicin, isoniazid and pyrazinamide. When fully sensitive Mycobacterium tuberculosis was grown on culture, the pyrazinamide was stopped. Treatment was continued for 6 months and the patient made a speedy recovery, with total resolution of his debilitating myalgia and weight loss. The creatine kinase returned to normal.
Box 1 Causes of myopathy/myalgia
Muscle involvement in tuberculosis, first reported in 1886, is rare. Only twelve other cases have been reported; and all but two presented with a focal muscle mass, abscess formation or pulmonary disease. To our knowledge there are only two case reports of proximal weakness as the predominant complaint in the absence of a muscle mass1,2. All previous reports describe pulmonary or direct muscle infection with M. tuberculosis. Our case is unusual in that there was no evidence of pulmonary or disseminated infection yet the symptoms were severe.
M. tuberculosis can cause a myopathy in several ways. There may be direct extension of infection into neighbouring muscle, as in psoas abscess formation, or haematogenous spread. An ill-defined polymyositis may also be seen, of unknown aetiology2. A muscle biopsy might have been of interest in our patient but was not done because his symptoms improved rapidly with treatment.