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A 29-year-old previously fit Asian man presented with a 3-month history of diffuse pain in the right thigh, with no obvious swelling or paraesthesia. He had no pyrexia, nocturnal sweats or any significant weight loss. He had no history of travel abroad nor had he any contact with tuberculosis. Physical examination revealed a thin man with a temperature of 37°C and no palpable lymphadenopathy. Systemic examinations were otherwise unremarkable. Examination of the right thigh did not reveal any tenderness or swelling but straight leg raising on the right was restricted to 40° (active) due to pain. Straight leg raising on the left was normal. There was no objective sensory impairment or abnormal reflexes in the lower limbs.
Initial investigations showed a haemoglobin of 11.8 g/dl with a mean corpuscular volume of 62.3 (thallassaemic trait). His white cell and differential counts were normal. Plasma viscosity was raised at 2.2 (normal range up to 1.7). The following tests were normal or negative: rheumatoid factor, antinuclear factor, immunoglobulin electrophoresis and quantitative immunoglobulin assay, blood culture and creatine kinase; C-reactive protein was elevated at 61.9 mg/1 (normal range 0–6). Radiographs of the chest, thoracic and lumbosacral spine and hip did not show any abnormality. An isotope bone scan (Tc99) was normal. Computed tomography (CT) of his lumbosacral spine failed to reveal any abnormality apart from a mild disc prolapse.
He was advised strong analgesics and physiotherapy and at review, 3 weeks later, an ill-defined painless fluctuant swelling on the right lateral thigh was discovered. A diagnostic aspiration revealed pus which was negative on Gram stain. Subsequent Zeil Nielson stain was also negative. An ultrasound scan of the right thigh showed extension of a cavity towards the right groin suggesting the possibility of a psoas abscess. A further CT scan of the abdomen (figures 1 and 2) failed to demonstrate any collection over the psoas or inside the pelvis and there was no connection with any intra-abdominal structure or the hip joint. However, the CT scan of the thigh muscles revealed a collection within the muscle planes of the glutei on the right extending to the right mid thigh (figure 3). A thoracic CT scan did not show any mediastinal, hilar or axillary lymphadenopathy. The lung fields were clear.
Seven hundred mls of pus was drained from the loculated swelling. There was no lymphadenopathy or intra-abdominal extension of the abscess cavity. The ‘cavity’ was loculated between the gluteus maximus and medius muscles.
- What do the CT scans in figures 1 and 2 show?
- What is the most likely diagnosis on the basis of the CT scan findings?
Figure 1 shows the normal outline of the psoas muscles with no evidence of intra-abdominal collection. Figure 2 shows a space-occupying lesion within the right gluteal region, which could either be an abscess cavity or a necrotic mass, not in communication with either a joint or intra-abdominal structure.
The most likely diagnosis is intramuscular abscess caused by a tubercular infection as the diagnostic aspiration yielded pus which as negative on Gram stain and also ordinary bacterial culture. The aspirated pus, however, showed profuse growth of acid fast bacilli, on culture. He was treated with rifampicin, ethambutol, isoniazid and pyrazinamide with complete resolution of his symptoms and no recurrence.
Primary intramuscular tubercular abscess is extremely rare and one should make a positive attempt to exclude intra-abdominal collection as psoas abscess may track down the groin or the thigh and present a similar clinical picture. It is not uncommon in patients who are immunosuppressed.
Primary skeletal muscle tuberculosis is extremely rare and earlier studies have reported only four cases of muscle tuberculosis in 2224 autopsy specimens from tubercular patients and one in 60000 cases of all types of tuberculosis.1 2 By far the commonest site of involvement of the skeleton is the spine (50% of cases), followed by hip and the knee. Our patient did not have any focal lesion on the spi-nal CT scan and there was no evidence of any psoas abscess.
The involvement of skeletal muscle in tuberculosis is usually by a direct extension from a neighbouring joint or rarely by haematogenous spread. The pathophysiological mechanism is not clear but it is possible that high lactic acid content of muscles, absence of reticulo-endothelial cells and lymphatic tissue in muscles associated with very rich blood supply may help towards the localisation of the bacteria in the muscles. Our patient was unusual as he had no systemic symptoms of any illness, no evidence of spinal tuberculosis, and no psoas abscess, which is one of the commonest presentations of swelling in the upper part of the thigh.
Discitis with or without psoas abscess is a common presenting feature in only 5–10% of cases of musculoskeletal tuberculosis. It is important to remember unusual presentations of tuberculosis in the appropriate racial background. It is important also to include symptomatic areas for scanning other than the typically described sites of spinal tuberculosis. Our patient was also somewhat unusual as he had no clinical or serological evidence of primary immune deficiency. He was neither a drug addict nor had any abnormal sexual behaviour. Although psoas abscess is a common cause of a swelling in the thigh, rare causes such as primary intramuscular tubercular abscess should also be considered in the differential diagnosis of painful swellings.
Intramuscular abscess caused by a tubercular infection.
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