Department of Rheumatology, Sunderland Royal Hospital, Sunderland SR4 7TP, UK
Correspondence to: N. D. Mckay. E-mail: drnmckay{at}hotmail.com
SIR, A 53-yr-old male Caucasian presented with a 12 h history of sudden-onset right hip pain, worse with movement, inability to weight bear and mild symptoms of urinary frequency. There was no history of recent travel, trauma or intravenous drug use. Past history included previous angioplasty for ischaemic heart disease, 56 units/week alcohol intake but previously 98 units/week, and seronegative RA treated with azathioprine and low-dose prednisolone for 8 years with excellent remission.
Examination revealed pyrexia 37.9°C and point tenderness over the right superomedial thigh and groin with absence of swelling or induration. There were no signs of active synovitis. Hip movements were globally restricted. Leucocytes were 13.5 x109/l with neutrophils 10.89 x109/l and haemoglobin 107 g/l. ESR was 147 mm/h, CRP 430 mg/l, creatinine kinase (CK) 15 U/l and urea and electrolytes was normal. Midstream urine, blood cultures (BC), and the Heaf test were negative. The right hip X-ray was normal. Isotope bone scanning revealed increased uptake in the inferomedial border of the right femoral neck as well as both knees, ankles, left elbow, left wrist and right shoulder. Subsequent MRI showed an abnormal bone marrow signal from the right femoral neck but no obvious features of osteonecrosis, synovitis or joint effusion. Surrounding soft tissue oedema in the iliacus muscle was, however, striking and compatible with presuppurative pyomyositis (Fig. 1).
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Pyomyositis is a primary infection of striated muscle traditionally recognized in tropical climates [13], where it is endemic and can account for up to 4% of surgical admissions [1]. Pyomyositis is increasingly reported in non-tropical populations, where the spectrum of clinical presentation, although poorly defined, is recognized to differ from that of tropical pyomyositis [4].
In the tropics pyomyositis is associated with eosinophilia, caused by Staphylococcus aureus in more than 90% of cases, rarely affects individuals aged over 55 yr, and predominates in children and adults aged 2045 yr. It has a good prognosis if diagnosed and treated [3].
In contrast, non-tropical pyomyositis consistently has an absence of eosinophilia, is caused by S. aureus in 65% of cases, can often affect older patients, and is associated with debilitating disease [4]. Specifically immunosuppressed states are associated with it, perhaps accounting for the increased reported mortality of 23% [4] and 7.7% [5] vs 0.52% in tropical pyomyositis [3].
Mortality increases with delayed diagnosis and the mean delay in diagnosis in the elderly or immunosuppressed states is 38.5 days [4], highlighting the importance of considering this condition in the at-risk population.
Pyomyositis can be divided into two clinical stages relating to abscess formation. The presuppurative stage is characterized by muscle pain, fever, malaise, raised inflammatory markers and leucocytosis. The affected muscle, if superficial, may be tender and have a firm, woody consistency but without a distinct mass [3]. Needle aspiration and culture at this stage does not reveal a causative organism [5]. The suppurative stage is heralded by fluctuance and a purulent collection, typically with a lack of local lymph node involvement. This suppuration may remain covert if a deep muscle is involved, e.g. the iliopsoas [6]. If it is unrecognized, pyomyositis can progress to sepsis and its complications which are sometimes referred to as a third stage. Any skeletal muscle site can be involved but inflammation of a single muscle in the thigh (60%) is typical.
The commonest presentation in a review of 97 patients with non-tropical pyomyositis is a male (75%) aged 43 yr with fever, initial stiffness or inflammation of a single muscle in the thigh, and, if cultured, S. aureus is isolated [4]. Additional features include a normal CK and negative BCs.
The pathogenesis of pyomyositis is unknown. Immunosuppressed states are a risk factor but in addition the affected muscle may have localized immunosuppression as Staphylococcus septicaemia is rarely associated with muscle abscesses [7]. Preceding viral infections of muscle and trauma have been linked to pyomyositis. Nutritional deficiency, especially of thiamine [8], can result in a biochemical lesion of the pyruvate oxidase system, subsequently lowering skeletal muscle immunocompetence. This case had a history of sustained high alcohol ingestion, which may have led to nutritional deficiencies. Although BCs are typically negative, bacteraemia is a necessary step in pyomyositis and a decreased ability in immunosuppression to combat bacteraemia could facilitate muscle infection.
Treatment consists of appropriate intravenous antibiotics and drainage of abscess if present. There is previously reported experience of complete resolution with antibiotics alone in tropical pyomyositis if therapy is commenced at an early stage [3].
The imaging, histological, microbiological, operation notes and the typical lateness of extramuscular involvement with pyomyositis suggest that the associated femoral head destruction was aseptic. The iliacus inserts into the psoas muscle tendon, which inserts into the femoral neck. Perhaps inflammation at this site interrupted the blood supply to the femoral head. The osteonecrosis of the hip may also be unrelated to the pyomyositis, given the existence of independent risk factors for this condition, although this appears the least likely.
Diagnosis requires clinical suspicion highlighting the importance of considering pyomyositis in the context of immunosuppression and thigh pain. This case illustrates the usefulness of MRI, which is sensitive for detecting subtle fascial and muscle signal changes as well as staging osteonecrosis. MRI criteria for pyomyositis help differentiate other causes of muscle tenderness and swelling, and can be used to monitor therapeutic response [9]. MRI should be the imaging modality of choice in suspected pyomyositis, and in this case it confirmed osteonecrosis, which is previously unreported in association with pyomyositis.
References