A 66-year-old woman presented with a 1-month history of a painful isolated mass on the inside of the left calf. She also complained of bilateral numbness in her toes. A history of contact with patients with suspected TB could be traced: her father had had pulmonary TB 10 years previously, and her daughter had had tuberculous pleurisy 7 years previously. She was in good general condition and did not complain of systemic symptoms such as night sweats, weight loss, anorexia, fatigue, or intermittent fever. Physical examination revealed a tender mass with irregular indistinct borders in her left calf. Movement was severely restricted by knee pain. She had a slight decrease in sensation and swelling of the lower extremities. The local temperature was not elevated, and the skin over the mass was normal. No obvious mass was palpable on the right leg. Further clinical examinations, including hemogram, erythrocyte sedimentation rate (ESR), procalcitonin test (PCT), liver and renal function tests, antinuclear antibody (ANA), antineutrophil cytoplasmic antibodies (ANCA), fungal G-test, and tumor marker levels, returned results within normal limits. Serological rheumatoid factor (RF) was elevated to 33.8 iu/ml (reference range: up to 15 iu/ml), serological high sensitivity C-reactive protein (CRP) waselevated to 7.48 mg/L (reference range: up to 3 mg/L), and antistreptolysin O (ASO) was positive. Tuberculin antibody IgG, IgM, gamma-interferon release test, purified protein derivative (PPD) skin test, acid-fast bacilli smear, and tissue culture of sputum were negative. Electromyography (EMG) indicated reduced motor and sensory nerve conduction velocity in the lower limbs (MCV: 25.8-33.1 m/s, SCV: 0-34.3 m/s), accompanied by decreased compound motor action potential (CMAP: 1.6-12.1 mV) and sensory nerve action potential amplitude (SNAP: 0-2.1 uV). Distal motor latency and F wave were normal. The duration and amplitude of motor unit potential (MUP) were increased, without spontaneous activity, indicating extensive chronic neurogenic lesions.
Chest computed tomography (CT) of case 1 revealed scattered bilateral inflammatory changes in the inferior lobes of both lungs and multiple nodular thickening on both sides of the pleura. Bilateral ultrasound of the calves suggested a 50 x 16-mm hypoechoic lesion in the left soleus muscle (Figure 1A) and a 43 x 6-mm hypoechoic lesion in the medial head of the gastrocnemius muscle. Additionally, 18 F-fluorodeoxyglucose positron emission tomography-computed tomography (18 F-FDG-PETCT) revealed multiple hypermetabolic lesions, which involved the left soleus muscle, the left musculus fibularis longus, the right soleus muscle, and the tibialis anterior muscle. The largest lesion was located on the middle of the left soleus muscle measuring 33.8 x 20 x 42 mm, and the maximum standardized uptake value (SUVmax) was 15.9 (Figure 1B). Magnetic resonance imaging (MRI) examination showed abnormal mass signals involving the inner front edge of the gastrocnemius muscle. The lesion was enhanced by gadolinium on the T1-weighted turbo spin-echo (T1W-TSE) image, and T2-weighted spectral presaturation attenuated inversion recovery (T2W-SPAIR) showed a hyperintense mass. There was a similar lesion in the gastrocnemius muscle of the right leg (Figures 1C, D). Pelvis and lumbar spine MRI showed mild lumbar disk herniation, with no other abnormal findings.
A muscle biopsy of the left gastrocnemius was performed in case 1; the result showed multiple nodular epithelioid granulomas embedded among the muscle fibers. Caseous necrosis was found under the microscope (Figure 1G). Microscopic examination for acid-fast bacilli stain and cytokeratin (AE1/AE3) was completely negative. CD3, CD31, CD34, desmin, Kp1, and PGM1 staining were weakly positive. The Ki67 labeling index was low (10%). PCR for the mycobacterium tuberculosis complex in blood, urine, sputum, and paraffin-embedded samples from case 1 returned negative results; however, the result was positive in frozen sections of muscles. A diagnosis of MT was considered in case 1, despite the fact that all the tests used for diagnosis of TB were negative, with the exceptions of PCR and histopathology.