Nuffield Orthopaedic Centre, Windmill Road, Oxford and 1 Battle Hospital, Oxford Road, Reading, UK
Correspondence to: C. Mukhtyar, Nuffield Orthopaedic Centre, Windmill Road, Oxford OX3 7EP, UK. E-mail: cbmukhtyar{at}hotmail.com
SIR, A 33-yr-old male presented with acute onset bilateral groin pain and fever reaching 40°C. He denied other systemic symptoms. Two days prior to presentation he had played a game of rugby.
On examination, he had several large psoriatic plaques, but none in the groin. Hip movements were painful but not significantly restricted. Spinal movements were unrestricted. A pelvic X-ray showed old calcification, probably representing previous gluteal haematoma. His white cell count was elevated at 15 x 109 /l and the CRP was 142 mg/l. An MRI (Fig. 1) of the pelvis demonstrated increased signalling within the left obturators, pectineus and adductors with contrast enhancement, but no abscess. Less marked enhancement was seen in the right obturators. Blood cultures grew Staphylococcus aureus sensitive to gentamicin and flucloxacillin.
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A recent review [2] of primary obturator pyomyositis identified only 22 English language reports, three of them from the UK. The diagnosis of obturator pyomyositis is commoner in youth; 18 of the now 23 case reports have been below the age of 16. S. aureus is the most frequent pathogen, accounting for 18 of the 23 reports.
Patients above the age of 30 with pyomyositis should be screened for immunosuppression [1]. Our patient did not suffer from diabetes mellitus or chronic liver disease. There was no history of i.v. drug abuse. In the absence of high-risk behaviour, HIV testing was not requested. Pyomyositis has hitherto occurred predominantly in the tropics but now seems to be occurring more frequently in temperate regions. The apparent increase of pyomyositis in general and obturator infections in particular could, however, reflect the improvement in imaging techniques. Only an imaging modality of great resolution, such as MRI with gadolinium enhancement, can delineate and identify a specific muscle in an anatomically complex region like the pelvis. The availability of MRI may therefore have contributed to increased recognition. It is the diagnostic modality of choice in primary obturator pyomyositis [13], clearly demonstrating diffuse muscle inflammation from the earliest stages of the disease.
Pyomyositis may occur if there is muscle trauma prior to a transient bacteraemia. This was shown by Miyake (1904) (cited by King et al. [2] and Viani et al. [4]) in animal studies following injection of sublethal doses of S. aureus. Myositis did not occur until the muscles were pinched, electrocuted or rendered ischaemic. Recent trauma or strenuous exercise has been noted shortly before the onset of symptoms in nine of the now 23 reports of obturator pyomyositis [2]. Of these nine patients, five had some form of skin lesion, which may have been the portal of entry for infection leading to muscle seeding.
Intravenous antibiotics are the mainstay of treatment, but no recommendations exist on the length of therapy, to our knowledge. However, where possible, drainage of collections is advisable. Occasionally, open drainage is required. Our patient received only antibiotics as the abscesses, discovered 3 weeks after the onset of i.v. antibiotics, were small, and clinical improvement had commenced. However, 10 of the other 22 descriptions of obturator involvement needed aspiration or open drainage [2].
Osteomyelitis is a recognized complication of pyomyositis in general [1] and ischial osteomyelitis has been reported in association with obturator pyomyositis [4]. Our patient has shown resolution of the abscesses with no evidence of osteomyelitis on follow-up MRI scans.
A new finding in our case is this patient's bilateral obturator involvement, a phenomenon not reported before. We have also documented the importance of repeated imaging in such a scenario. Single imaging would have missed the development of bilateral changes. Obturator pyomyositis is an important differential diagnosis of acute pelvic pain.
References
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