Tuberculous pyomyositis presenting as septic arthritis and multiple site pyomyositis

Abstract

Primary tropical pyomyositis, commonly caused by Staphylococcus aureus, is characterised by suppuration in skeletal muscles, which manifests as single or multiple abscesses. Another rare causative organism is Mycobacterium tuberculosis in endemic areas. Here, we report a case of primary tuberculous pyomyositis presenting as septic arthritis of the right knee and multiple site pyomyositis of the right thigh and chest wall. A tuberculous aetiology was overlooked at first, which resulted in a diagnostic delay. The patient was initially diagnosed, using ultrasonography, MRI and an absence of systemic symptoms of tuberculosis, with bacterial pyomyositis and treated with broad-spectrum antibiotics. However, further investigations performed on knee joint aspirate yielded negative cultures and a positive cartridge-based nucleic acid amplification test, which, along with a non-resolution of his symptoms, suggested a primary tuberculous pyomyositis. He was successfully managed with incision and drainage of the lesions and completion of anti-tubercular therapy.

Background

Primary pyomyositis is defined as a primary, subacute, deep-seated bacterial infection affecting skeletal muscles.^1–4 It is alternatively known as ‘infective myositis’, ‘pyogenic myositis’, ‘suppurative myositis’, ‘myositis purulenta tropica’, ‘epidemic abscess’ or ‘bacterial myositis’ based on regional prevalence.¹ Although it primarily occurs in the tropics, it is more frequently encountered in temperate regions.^{4 5} Staphylococcus aureus is the most implicated organism.1 2 5 6 Tuberculous pyomyositis is the term used when the microorganism responsible for the infection is Mycobacterium tuberculosis.⁷ Musculoskeletal involvement occurs in about 3% of patients with tuberculosis (TB), predominantly spondylitis, osteomyelitis or arthritis.^{8 9} Primary tuberculous pyomyositis as an independent entity has rarely been discussed in the literature and constitutes less than 1% of musculoskeletal TB cases.⁷ Due to the rarity of the disease, lack of specific signs and symptoms and often culture negativity, tuberculous pyomyositis tends to be overlooked at the time of initial diagnosis.

Case presentation

A male in his 50s presented to our General Medicine outpatient department with a 3-day history of pain and swelling in the right lower limb as well as a 1-week history of difficulty in walking. He also reported a 4-day history of abdominal distension, which was insidious in onset and gradually progressive. It was not associated with pain. The patient also complained of shortness of breath, which was consistent with orthopnoea. There was no history of trauma to the affected areas. He had a medical history of chronic liver disease, pulmonary hypertension, type 2 diabetes mellitus, systemic hypertension and cervical spondylosis (C2–C6 radiculopathy). There was no significant medical history in his family. He had a history of alcohol abuse 3 years ago. A history of an altered sleep-wake cycle was also elicited. On examination, he was conscious, cooperative and well-oriented to time, place and person. His pulse was 90 beats/min; blood pressure, 110/70 mm Hg; respiratory rate, 18 breaths/min; and SpO₂, 99% on room air, and he was afebrile. Head-to-toe examination revealed pallor, icterus and pedal oedema. On admission, respiratory, neurological and cardiovascular examinations revealed no abnormalities, and abdominal examination revealed a distended abdomen with dilated veins over it along with a positive fluid thrill. Routine investigations revealed elevated white cell counts: neutrophil predominant with peripheral smear suggestive of infection along with an elevated CRP level (137.12 mg/L). Seeing this, the patient was started on empirical antibiotics (details are given in the treatment section and figure 1). Following hospitalisation, the patient developed pain in the left upper chest. Local examination of the region revealed a 5×3 cm swelling in the left infraclavicular region, which was cystic, tender and fluctuant, with no erythema, local increase of temperature or pus point. To evaluate the chest pain, contrast-enhanced CT (CECT) of the chest was done (figure 2A–C), which revealed an irregular heterogeneously hypodense collection showing mild peripheral enhancement along the left upper chest wall, with intrathoracic and extrathoracic components, communicating along the first intercostal space, which was suggestive of an abscess or necrosis. Doppler ultrasonography (USG) was done on the right lower limb, which was suggestive of cellulitis. The Department of Surgery was consulted for the management of the same, and the patient was managed with incision and drainage of the chest wall granuloma, the pus from which was sterile. However, after a few days, the patient complained of severe pain in the right thigh and a repeat USG showed a large ill-defined hypoechoic area in the anterior deep intramuscular plane. An MRI of the knee was done to confirm the findings, which suggested mild joint effusion with extensive thickening and enhancement of synovium with reduced femorotibial joint space, cortical irregularities and marrow oedema of the bilateral condyles of the femur and tibia, suggested septic arthritis affecting the knee along with a multiloculated intramuscular abscess or necrosis abutting the distal half of the femoral shaft surrounded by extensive myofascial oedema, which was suggestive of pyomyositis (figure 3A–D). The tissue from the right thigh obtained during incision and drainage was sent for histopathological examination, which revealed fibro-collagenous stroma and fibroadipose tissue bits with a dense mixed inflammatory infiltrate of lymphocytes, plasma cells, neutrophils, foamy macrophages and numerous proliferating blood vessels lined by plump endothelial lining as well as a focal area of dystrophic calcification, suggestive of the granulation tissue. A few days later, the USG of the right thigh was repeated, which showed the resolution of the collection. The patient also improved symptomatically and was able to mobilise the limb again. The patient was hence discharged and asked to review in the clinic with reports. On follow-up, the patient seemed better overall. However, the knee pain and swelling persisted, and the cartridge-based nucleic acid amplification test (CBNAAT) done on the joint aspirate showed positivity for M. tuberculosis.

Figure 1.

Timeline of events created by Dr Meghna Somaraj.

Figure 2.

(A) contrast-enhanced CT (CECT) thorax-sagittal plane showing chest abscess with intrathoracic and extrathoracic extension, communicating through the first intercostal space. (B) CECT thorax-transverse plane showing chest abscess with extrathoracic and intrathoracic components. (C) CECT thorax-coronal plane showing chest wall abscess with intrathoracic and extrathoracic components.

Figure 3.

(A) MRI of the right thigh and knee – sagittal plane showing pyomyositis showing septic arthritis of the knee. (B) MRI of the right thigh and knee – cross-sectional view showing that abscess mainly involves the vastus medialis and vastus intermedius. (C) MRI of the right thigh and knee – sagittal plane showing pyomyositis. (D) MRI of the right thigh and knee – coronal plane showing multiloculated collection.

Investigations

Chest wall granuloma aspirate proved to be sterile on gram stain and bacterial culture.

Differential diagnosis

Our first differential diagnosis was necrotising fasciitis since the patient had a history of diabetes mellitus, and there was swelling, pus and difficulty in mobilising the limb. However, the MRI scan led us in the right direction and allowed us to localise the lesion to the muscle, thereby ruling out necrotising fasciitis. On this, we immediately thought of staphylococcal tropical pyomyositis, as that is the most common agent, and the presentation indicated the same. However, the negative cultures led us to understand that it was an unlikely diagnosis.

Treatment

The initial revelation of elevated white counts as well as inflammatory markers prompted the start of cefoperazone-sulbactam along with clindamycin (figure 1). Once lower-limb USG revealed cellulitis, conservative management was started for the same with topical magnesium Sslphate and a combination of vancomycin with piperacillin-tazobactam. The chest wall lesion detected on CECT was promptly incised and drained due to severe pain. He was found to have a fever postoperatively, which was managed by escalating the antibiotics to cefepime. For the treatment of thigh granuloma and septic arthritis, the patient underwent incision and drainage yet again along with knee exploration, and the aspirate was sent for analysis. Since the patient had a history of chronic liver disease, he developed massive ascites, which was managed with an ascitic tap. His blood sugar levels and blood pressure were also adequately managed using appropriate medications. Once the diagnosis of tuberculous pyomyositis was confirmed on follow-up, the patient was started on anti-tubercular therapy with isoniazid, pyrazinamide, ethambutol and rifampicin, which was continued for 6 months, on the completion of which we saw a complete return to his full functional status.

Outcome and follow-up

There was a drastic improvement in the patient’s condition. The pain and swelling finally subsided, and he regained full mobility in the limb following anti-tubercular therapy. This finally put an end to his symptoms. He has been on regular monthly follow-ups ever since, and there has been no recurrence of his condition.

Discussion

Tropical pyomyositis is not an uncommon disease in India. It manifests in all age groups but has been most prevalent in males between ages 10 and 20 years. Individuals aged over 30 years who develop pyomyositis often have underlying diseases or conditions that may compromise the immune system such as ‘diabetes mellitus, chronic kidney disease, asplenia, scleroderma, rheumatoid arthritis, HIV infection and AIDS and Felty syndrome’.^{1 10–12} S. aureus is responsible for about 75% of the cases of pyomyositis, followed by Streptococcus (10–15%).^{6 11} Case reports where M. tuberculosis is the causative agent of pyomyositis have been documented less frequently.^{8 13} The rare occurrence of this disease is demonstrated by a study conducted by Wang et al in 2003 where tuberculous pyomyositis accounted for only 1.8% (21 out of 1153) of culture-positive TB cases in Taiwan.^{8 13} Many of these cases involved a single site and had other manifestations of TB. In another study conducted by Zeng et al reviewing 19 patients aged over 19 years, 63.2% (12 patients) presented manifestations at single sites, and 7 patients had manifestations at multiple sites, including the thigh, calf, arm, chest wall, dorsal, psoas, gluteal and forehead muscles.¹⁴ Here, we report a patient with multiple site tuberculous pyomyositis involving the chest wall and thigh muscles (vastus medialis and vastus intermedius), with no other manifestations of TB, which was complicated by septic arthritis of the right knee joint.

Muscle involvement in M. tuberculosis infection is exceedingly uncommon due to protective factors. These include elevated lactic acid content of the muscles, the absence of lymphatic and reticuloendothelial tissues, the well-differentiated nature of muscles and its robust vascular supply.¹⁵ Infection with M. tuberculosis usually targets single large muscles in the upper and lower limbs, such as the quadriceps femoris, gastrocnemius, adductor longus/magnus, brachioradialis, flexor digitorum superficialis/profundus, biceps and triceps. Differing perspectives exist among authors regarding muscular TB of the muscle. Some authors propose that the skeletal muscle becomes involved because of M. tuberculosis infection in surrounding structures,¹⁶ while others contend that TB affecting the muscles is the primary site of infection.¹⁷ While the exact mechanism of pathogenesis remains unclear,1 3 6 18 a prevailing notion indicates that the infection is likely a consequence of transient bacteraemia in individuals with concurrent muscle abnormality. Uninjured skeletal muscles are postulated to be resistant to infection.^{1 6 19} Other possible mechanisms include trauma to the affected muscle, followed by a haematogenous invasion by bacteria^{1 6} and contiguous spread from the adjacent bone or soft tissue infection.⁸

Pyomyositis typically presents as a localised abscess or necrosis but may also present as a diffuse inflammatory or rapidly progressive myonecrotic process.⁶ Zeng et al found that muscular TB generally had an occult, chronic onset that gradually aggravated over time.¹⁴ The clinical manifestations are varied and vague.^{6 8 13} Typical symptoms of M. tuberculosis infection may or may not be present. Many times, the only symptoms on presentation include fever, ill-defined swelling or local masses and pain with or without a limp in the affected extremities. The symptoms mimic many other musculoskeletal infective conditions, making the diagnosis difficult based on the clinical presentation alone. The disease progresses in three stages, as illustrated in table 1. Stage 3 is the most severe and is accompanied by systemic toxicity, with patients developing complications such as bacteraemia, and studies by Wang et al have shown mortality rates as high as 14% due to uncontrolled sepsis.^{6 8 13}

Table 1.

Stages of tropical pyomyositis²⁵ created by Dr Meghna Somaraj

Stage no.	Name of the stage	Symptoms	Signs	Other findings
1	Invasive stage	Low-grade fever, malaise, pain	The muscle has a woody texture on deep palpation	Leukocytosis
2	Suppurative phase	Fever, swelling, erythema	Abscess/granuloma can be felt	Lasts about 1–3 weeks; most patients present at this stage.
3	Late Stage	High fever, septicaemia, renal failure and other systemic manifestations	Clinical deterioration in signs	Mortality of about 10%

The diagnosis of pyomyositis is typically established by radiographic imaging, with USG and MRI being the primary modalities used. Characteristic findings on MRI showing a well-demarcated abscess or necrosis with rim enhancement can help distinguish it from other soft tissue masses.²⁰ Aspiration of the swelling, followed by sending obtained aspirate for gram staining, acid-fast bacilli (AFB) staining, culture and sensitivity help confirm the aetiology. Demonstration of AFB on Ziehl-Nielsen stain may further confirm the diagnosis; however, in case of low bacterial load in the lesion, the aspirate may be negative for AFB staining despite it being an M. tuberculosis infection.⁷ CBNAAT can also be done to detect extrapulmonary tuberculosis (EPTB). However, it has a low negative predictive value, and its negativity does not rule out the disease effectively.²¹

The treatment for pyomyositis depends on the stage of presentation. The management for stage 1 is purely medical, while stages 2–3 require medical treatment with surgical intervention.1 6 8 13 Stage 1 can be treated with broad-spectrum antibiotics to cover both gram-positive and gram-negative pathogens as well as anaerobes. In stages 2 and 3, the treatment approach involves performing an incision and drainage of the muscle abscess, followed by a course of antibiotic treatment. The duration of treatment is determined by the organisms involved and the complications present.^{6 13} Timely treatment usually results in complete recovery. Tuberculous pyomyositis should be suspected when a patient presents with a swelling of insidious onset and slow progression,⁷ negative cultures for other organisms and failure of the course of antibiotics with disease recurrence.^{8 13} Culture of M. tuberculosis is the gold standard for diagnosis. CBNAAT may be used as a screening tool, which will further aid in the diagnosis.²² The absence of AFB staining and culture from the aspirates is a limitation in the present study. Nevertheless, we obtained a positive result with CBNAAT, which directed our diagnosis towards a tuberculous aetiology. For confirmed primary EPTB, the treatment is the same as pulmonary TB with a long course of anti-tubercular treatment (ATT). The treatment is a four-drug regimen (isoniazid, rifampicin, pyrazinamide and ethambutol) for 6 months.²³ Immediate and vigilant initiation of ATT can prevent dangerous complications and disease progression to septic stages.^{8 13}

Because of its ambiguity and vague clinical manifestations, which can be attributed to other diseases, tuberculous pyomyositis is often missed in the differentials during initial diagnoses.^{1 6 13} Furthermore, if the affected muscle is deep-seated and local signs are not evident, the diagnosis could be delayed. Such a delay may result in the disease progression to later stages and pose treatment challenges.⁶ Some complications due to a late diagnosis include adjacent joint infection, sepsis and occasionally death.^{18 24} Long-term sequelae include osteomyelitis of the adjacent bones, muscle scarring, residual weakness and functional impairment.^{1 6} Additionally, cases of granulomatous inflammation in the lung and brain, pericarditis, myocarditis, endocarditis and renal failure have also been documented. Therefore, clinicians must enhance their familiarity with the mode of presentation of this potentially life-threatening disease and include it in their differentials of musculoskeletal diseases, with TB as a possible aetiology. Early recognition and timely treatment are the key and could be lifesaving. Once suspected, the management of this entity is not particularly challenging. In our case, clinicians’ suspicion, effective drainage of the lesion and timely start of ATT resulted in the complete clinical recovery of the patient.

Learning points.

• Tropical pyomyositis must be considered as a differential diagnosis whenever signs and symptoms point towards musculoskeletal infection.

• It may occur concurrently with or lead to septic arthritis of the adjacent joint.

• An MRI should be obtained at an early stage, and an early diagnosis should be made to facilitate early treatment with surgical drainage and antimicrobial agents and a complete recovery. Late diagnosis may lead to complications such as sepsis and increase long-term effects and even mortality.

• TB must be considered an important aetiology for tropical pyomyositis in endemic areas, and treatment in the form of incision and drainage as well as starting ATT must be done at the earliest.

• The patient must also be closely followed up to determine the efficacy of the treatment as well as to help correct precipitating causes, if any.

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