Stage 3 pyomyositis of the gluteus minimus; Staphylococcus aureus sepsis, autoanticoagulation, proximal femoral osteomyelitis and the role of surgical intervention

Abstract

Primary pyomyositis is a rare bacterial infection of the skeletal muscle. Traditionally a tropical disease, it is increasingly described in westernised urban populations. The aetiology is due to transient bacteraemia in the presence of risk factors such as traumatised muscle, or immunocompromise. The condition presents in one of three stages, representing progression of disease severity. Intravenous antibiotic therapy is often sufficient for this disease at its early stage, but surgical drainage is necessary for advanced presentations. We report a severe case of stage 3 pyomyositis of the gluteus minimus, which led to Staphylococcus aureus sepsis, deranged liver function, acute kidney injury, autoanticoagulation and proximal femoral osteomyelitis in a healthy 64-year-old Caucasian man. This illustrates the potential severity of the disease, the life-threatening sequelae when diagnosis is delayed and the role of surgical drainage in averting the progression of systemic sepsis to end-organ dysfunction, disseminated intravascular coagulation and potentially death.

Background

Primary pyomyositis is a rare, subacute, bacterial infection of the skeletal muscle. Traditionally regarded as a tropical disease common to parts of Africa and the South Pacific,¹ it is increasingly being described in westernised urban populations.^{2 3} Most common in the first and second decades of life, it can affect all age groups and shows a slight male predominance.^{1 4 5} Any muscle group can be affected most commonly a single muscle in the pelvic girdle or lower extremity, although 11–43% of patients have multiple site involvement.^{1 5}

The aetiology is considered to be due to transient bacteraemia in the presence of risk factors such as traumatised muscle, or immunocompromise.^{2 6–8} The condition presents in one of three distinct stages, which represent progression of the disease severity.⁵ Stage 1 begins with low-grade fever, malaise and myalgia, but can often remain subclinical delaying presentation. Stage 2 is focal muscle abscess formation with progression of both local and systemic signs of inflammation, without treatment the condition will progress to stage 3 with increase in the severity of local inflammation, the development of septic shock⁵ and systemic complications such as renal failure, disseminated intravascular coagulopathy (DIC) and acute respiratory distress syndrome.⁶ The most commonly isolated organism is Staphylococcus aureus, but streptococci, Salmonella and Mycobacterium tuberculosis have all been implicated.⁶

Treatment depends on the severity of the disease at presentation. Intravenous antibiotic therapy is often sufficient for early-stage disease, but once an abscess has formed it will require drainage, either percutaneously or via an open surgical approach.^{3 5 9} In the majority of cases the described treatments result in complete recovery, however osteomyelitis, muscle scarring and functional impairment have all been reported.^9–11

We report a severe case of stage 3 pyomyositis of the gluteus minimus, which led to S aureus sepsis, deranged liver function, acute kidney injury, autoanticoagulation and proximal femoral osteomyelitis in a healthy 64-year-old Caucasian man.

Case presentation

A 64-year-old fit and well Caucasian man presented with a 1-week history of left hip pain, which he first noticed while on a walking holiday in the Lake District. The patient localised the pain to his groin and buttock, and described an insidious onset over the course of the week. He was initially well, but subsequently developed malaise and lethargy.

On examination he had pain on palpation around the greater trochanter and the adductor region, but a full, pain-free range of motion in the hip, although he was unable to straight leg raise due to pain. On admission he was initially non-feverish, but subsequently developed persistent fever of over 38°C.

Investigations

Initial haematological and biochemical investigation revealed a white cell count of 5.5×10⁹ /L, a C reactive protein (CRP) 353 mg/L and an international normalised ratio 1.6, unusual as the patient was not on any form of anticoagulation. Liver function tests showed a raised alanine aminotransferase (ALT) of 108 µg/L and alkaline phosphatase of 157 ug/L. Blood cultures grew a methilicillin-sensitive S aureus (MSSA).

Plain radiographs of the hips and pelvis showed evidence of osteoarthritis in the left hip, but nothing to explain the clinical picture. MRI demonstrated an abscess with the gluteus minimis with oedema of the illiacus and psoas muscles (figure 1).

Figure 1.

Coronal T1 gadolinium-enhanced MRI showing an abscess in left gluteus minimus and extensive inflammatory changes in surrounding muscles.

Differential diagnosis

Septic arthritis, osteomyelitis.

Treatment

The patient underwent an open washout and debridement of the left hip on the day after admission, which revealed a large collection of frank pus within the gluteus minimis muscle. This collection was evacuated, the cavity washed out and a drain was left in situ for 48 h. Microscopy and culture of the pus samples grew MSSA, identical to the bacteria isolated in blood cultures, and the patient was started on 2 g intravenous flucloxacillin every 6 h.

Surgery successfully reduced the patient's bacterial load, and his systemic inflammatory response syndrome resolved, but his postoperative course was far from straightforward. The appearance of splinter haemorrhages on his left index finger raised the possibility of infective endocarditis as a primary pathology, but transoesophageal echo later disproved this. A liver ultrasound was performed, owing to the patients transaminitis and clotting abnormality, showing normal liver architecture, but did note an enlarge spleen. A raised serum ferritin suggested haemochromatosis, but this subsequently returned to normal; further investigation for haemochromatosis did not yield any positive findings.

On the 10th day of treatment with intravenous flucloxacillin the patient developed a widespread maculopapular rash, thought to be a drug hypersensitiviy reaction, so flucloxacillin was discontinued and intravenous vancomycin with oral rifampicin was intitiated. The patient showed a good initial response, but then reached a plateau phase, and 4 weeks post initial surgery still had significantly raised inflammatory markers with CRP 99 mg/L. Repeat MRI demonstrated extensive inflammatory changes in all gluteal muscles and osteomyelitis of the proximal femur, but no pus collection.

The patient remained on intravenous therapy for a further 2 weeks, making 6 weeks in total, and then was switched onto oral ciprofloxacin and rifampicin facilitating his discharge home.

Outcome and follow-up

The patient remained on oral antibiotics for 3 months in the community at which point was returning to his premorbid level of mobility, with no evidence of relapse, his CRP at this stage was 3. Repeat MRI 3 months postdischarge showed considerable reduction in the bone marrow oedema within the femoral head and neck, and resolution of the inflammatory changes in the surrounding musculature.

Discussion

The case described here is certainly not typical of primary pyomyositis in terms of patient characteristics, disease severity, progression and response to established treatment.

Pyomyositis patients over 30 years of age commonly have an underlying condition causing immunocompromise, such as HIV, diabetes mellitus or chronic renal/liver disease.¹² Non-tropical pyomyositis, described by Hossain in New York, is also associated with an underlying risk factor for poor immune function, with 75% of his affected population being affected by HIV, intravenous drug use, malnutrition, diabetes or chronic renal failure.³ Trauma is often implicated in the development of pyomyositis, as even in the presence of bacteraemia structurally normal muscle will remain uninfected.² Trauma to the affected muscle is believed to cause structural alterations creating a locus minoris (a place of diminished resistance) for the implantation of bacteria.¹³

Our patient was thoroughly investigated for an underlying cause to no avail; an HIV test was negative and there was no evidence of diabetes, biochemical markers of kidney and liver function returned to normal after initial derangement and structural liver or kidney abnormality was ruled out with ultrasound and CT imaging.

The degree of systemic complication in this case was also unusual, a stage 3 presentation with abscess formation, septic shock, evidence of end-organ dysfunction and a clotting abnormality which may represent early DIC.

Open surgical drainage has been the traditional approach, with a large incision allowing good exposure, drainage and debridement under direct vision. Recently, an ultrasound or CT-guided percutaneous drainage have been successfully utilised.¹⁴ This method of treatment was not considered in this case due to the severity of the patient's condition and the need to ensure optimum drainage and debridement.

Isolation of a methicillin sensitive S aureus is one feature of this case that is typical, as all large series report S aureus to be the most commonly isolated organism, causing the disease in 77% of cases.⁵ Given that the causative organism was easily isolated, and that it was sensitive to conventional antimicrobial therapy, it is unusual that such a prolonged course of intravenous therapy was required. Further imaging demonstrated that the inflammatory process was still very active, and had progressed to cause proximal femoral osteomyelitis. At this point the question of further surgical intervention was raised, but given the lack of a defined collection the risks of surgery outweighed the potential benefit.

Learning points.

• Pyomyositis is an important differential in the septic patient with musculoskeletal symptoms.

• Pyomyositis is a potentially life-threatening condition with potential for progression to systemic sepsis, disseminated intravascular coagulation and even death.

• Timely surgical intervention is necessary when abscess formation has occurred.

• Open surgical techniques can be beneficial when compared to CT-guided drainage in an unwell patient.