Tuberculous Pyomyositis: A Rare but Serious Diagnosis

Introduction

Tuberculous pyomyositis is a rare manifestation of extrapulmonary tuberculosis and may lead to significant morbidity if diagnosis is delayed.

Early recognition of tuberculous pyomyositis is extremely important, especially in endemic regions to prevent severe complications.

Case Presentation

A 29-year-old male presented with a three-month history of progressive left thigh pain, swelling, and intermittent fever. The pain began as a dull ache in the mid-thigh and gradually worsened, leading to significant functional limitation and eventual inability to walk. The swelling developed approximately 20 days after onset of pain and progressively increased in size. He also reported intermittent low-grade fever with chills (maximum 102°F), anorexia, and weight loss. Additionally, he had a 20-day history of dry cough without sputum or hemoptysis. There was no history of trauma or known tuberculosis exposure.

He was initially treated with intravenous antibiotics without improvement in Malaysia and was subsequently transferred to Yangon General Hospital.

On examination, his temperature was 100°F, blood pressure 110/62 mmHg, pulse 78 beats/min, respiratory rate 18 breaths/min, and oxygen saturation 98% on room air. Chest examination was unremarkable. Abdominal examination was normal. Local examination of the left thigh revealed a diffuse, tender swelling over the anteromedial aspect measuring approximately 16 cm. No peripheral lymphadenopathy was noted.

Initial laboratory values are summarized in Table 1.

Diagnostic Workup and Evaluation

The patient was admitted to the general medical ward and started on empiric broad-spectrum antibiotics. CT imaging of the left thigh demonstrated bony expansion with mixed lytic–sclerotic lesions involving the left greater trochanter and femoral shaft, with sinus tract formation suggestive of chronic osteomyelitis, along with multiple intramuscular abscesses in the left thigh muscles (Fig.1). Chest X-ray revealed a thin-walled cavity in the right upper lobe (Fig. 2). Intravenous vancomycin and metronidazole were initiated according to pus for C&S. MRI of the left thigh confirmed chronic osteomyelitis with bone marrow edema and intramedullary abscesses (Fig. 3). Subsequently, bone marrow trephine biopsy showed mild myeloid and megakaryocytic proliferation, with no evidence of acid-fast bacilli or fungal elements. Despite appropriate antibiotics, no clinical or radiological improvement was noted.

Ultrasound-guided drainage of the thigh abscess was performed, and a catheter was placed (Fig 4). Pus samples were sent for culture and Ziehl–Neelsen staining. Smear of the aspirate was positive for acid-fast bacilli (Fig. 5). The drainage catheter was removed after 15 days.

Empiric antibiotics were discontinued, and standard anti-tuberculous therapy (isoniazid with pyridoxine, rifampicin, pyrazinamide, and ethambutol) was started. After two week of treatment, the patient became afebrile with significant clinical improvement. After 2 months at follow-up, he was able to walk independently without pain.

Fig. 2 : CXR finding: (arrow) cavity in right upper lobe

Fig. 3: MRI finding of left thigh -chronic osteomyelitis with bone marrow edema and intramedullary

Discussion

Tuberculosis (TB) remains one of the leading infectious causes of morbidity and mortality worldwide. According to the World Health Organization, an estimated 10.7 million people developed TB in 2025, and approximately 1.23 million deaths were attributed to the disease globally. ^1. Extrapulmonary tuberculosis accounts for approximately 40% of all TB cases, most commonly involving the lymph nodes and abdomen. Most cases verified to have a previous pulmonary TB origin. TB bacilli spread over the pleural cavity, starting from a pulmonary infection focus on that occasion, immigrates through the blood vessels or lymphatics to other organs developing extrapulmonary TB. Musculoskeletal tuberculosis is uncommon, representing about 3% of cases, with spondylitis, osteomyelitis, and arthritis being the typical forms. Tuberculous pyomyositis is even more extremely rare, with a reported incidence ranging from 0.015% to 2%, often posing diagnostic challenges in clinical practice ².

Most common cause of tuberculous pyomyositis is typically caused by invasion from adjacent structures rather than by primary infection, hematogenous seeding or lymphatic spread. The prevalence of tuberculous pyomyositis is more common in immuno-deficient patients and associated with the use of corticosteroids, the presence of HIV infection, the administration of cancer chemotherapy, and renal failure ³.

Though the muscle involvement is rare in Mycobacterium tuberculae infection and there is possible explanations for the rarity of muscle involvement in tuberculosis include the high lactic acid content of the muscle which is unfavourable for growth and multiplication of tubercle bacilli, absence of lymphatic tissue and reticulo-endothelial tissue, well differentiated state of muscular tissue, and its good vascular supply ^4.

Clinically, TB pyomyositis presents insidiously over weeks to months with progressive swelling, dull aching pain, and low-grade fever without the erythema and acute tenderness characteristic of bacterial pyomyositis. ^5. This cold abscess phenotype is the key clinical differentiator and was consistently observed in this case. The systematic review by Horai et al. (2023) confirmed that swelling was present in 93.8% and intramuscular abscess in 79.6% of adult isolated tuberculous myositis cases, with a median symptom duration of 75 days in immunocompetent patients , closely mirroring this patient’s three-month history. ⁶

Diagnostically, plain radiography revealed cortical lytic destruction of the femur, while NECT confirmed mixed lytic-sclerotic osteomyelitic lesions with sinus tract formation and multiple deep intramuscular abscesses. MRI provided the highest soft-tissue resolution for delineating abscess extent. Thammaroj et al. demonstrated that TB pyomyositis on MRI is characterised by the absence of T2-hyperintense abscess walls and a higher association with spinal and psoas muscle involvement, contrasting with bacterial pyomyositis. ⁷ The gold-standard diagnostic confirmation was achieved by AFB positivity in the aspirated pus, underscoring that microbiological examination of drained material is indispensable. ⁵ Initial empirical antibiotics yielded no improvement which is a critical red flag that should prompt active consideration of TB in any patient from an endemic region with an unresponsive pyomyositis. ^5,8

Management comprised four-drug anti-TB therapy (isoniazid, rifampicin, pyrazinamide, ethambutol) for 12 months, consistent with WHO guidelines for musculoskeletal TB with bony involvement. ¹ USG-guided drainage of the intramuscular abscesses provided both therapeutic decompression and diagnostic material. Ahmad et al. reported that 57% of TB pyomyositis patients required surgical or image-guided drainage alongside anti-TB chemotherapy, with uniformly satisfactory outcomes. ⁹

With prompt initiation of targeted anti-TB therapy and abscess drainage, the patient demonstrated clinical improvement, consistent with reported treatment success rates of 89.4% in the literature. ¹⁰ However, delayed diagnosis remains the principal determinant of poor outcomes, including multiorgan failure and death. ⁸ This case reinforces the imperative of maintaining TB as a differential diagnosis in patients from endemic regions presenting with chronic pyomyositis unresponsive to conventional antibiotics.

REFERENCES

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Author Information

Si-Htoo-Aung¹, Ni-Ni-Aung², May-Kyi-Oo³, Min-Zaw-Oo⁴

1. Specialist Assistant Surgeon, Department of Medicine, Yangon General Hospital,Yangon
2. Junior consultant physician, Department of Medicine, Yangon General Hospital,Yangon
3. Senior Consultant physician, Department of Medicine, Yangon General Hospital,Yangon
4. Professor, Medical Unit (3), Department of Medicine, Yangon General Hospital,Yangon