Working Diagnosis:
Primary pyomyositis of the right iliacus and piriformis muscles of idiopathic origin.

Treatment:
Oral antibiotics:
Bactrim double strength twice daily
for 3 weeks.
Gait training and non-impact
conditioning.
Osteopathic manipulative treatments.
Progressive strengthening and conditioning with impact and sport specific drills.

Outcome:
The patient noticed a reduction of pain within 24 hours of starting antibiotics. The patient was able to complete treatment with only oral antibiotics, avoiding hospitalization. Due to deconditioning of the involved and surrounding musculature of the hip, the patient did require significant rehabilitation to return to baseline. He had a full recovery with return to play for basketball 5 weeks after starting antibiotics.

Author's Comments:
Primary pyomyositis is a rare infection of a skeletal muscle. Pyomyositis was classically described in immunocomprimised individuals or those with other risk factors such as intravenous drug use. The diagnosis is usually delayed due to low suspicion, elevation of non-specific markers and a physical exam which may be mistaken for other diagnoses. Typically a fluid collection is present on imaging by the time the diagnosis is made. This requires treatment with percutaneous or surgical drainage and IV antibiotics.
In the last 15 years, there has been increasing incidence of pyomyositis in young, healthy patients with no risk factors. Community-acquired methicillin-resistant staphylococcus aureus (ca-MRSA) has been found as the cause in up to 90% of these cases. It is hypothesized this process begins as a transient infection in the setting of muscle injury or overuse.
Our case utilized an early MRI, demonstrating isolated edema within the muscle and no fluid accumulation. Due to the high incidence of ca-MRSA, Bactrim was selected for treatment. The diagnosis is rarely made in stage 1. Diagnosis at this early stage allows the patient to be treated as an outpatient with an oral antibiotics, avoid invasive procedures, and decrease morbidity and mortality.

Editor's Comments:
Pyomyositis represents a broad range of infections including bacteria, fungal, parasitic, and viral causes. As the author noted, bacterial pyomyositis is frequently caused by staph aureus, with 50-75% MRSA rates depending on region. Although no source of infection is identified in primary pyomysitis, retrospective analysis has established an association with trauma. Immunocompromise and intravenous drug use are other commonly associated risk factors. This patients presentation and his recent history of a football game make trauma the likely source of his infection due to a small puncture wound at some point in the game. If he is like most high school football players, his risk may have been augmented by the lack of regular washing of his gear.
Pyomyositis is often missed in the early stages of infection represented by swelling, mild pain, and subacute fevers over a period of 1-3 weeks. In stage 2 the fevers and localized pain become more pronounced, and the diagnosis is often made at this time. Stage 3 is characterized by sepsis and systemic symptoms.
Dianosis is typically established by elevated CBC, ESR, and MRI. Differential diagnosis includes osteomyelitis, septic arthritis, thrombosis, hematoma, or muscle strain. Pyomyositis typically affects a single muscle group, most commonly the gluteus or quadriceps muscles. Psoas abcesses are considered a separate clinical entity from pyomyositis and are usually caused by hematologic spread. Initial broad spectrum treatment requires coverage of MRSA, gram negative, and anaerobes. Most stage 2-3 infections require hospitalization for IV antibiotics and possibly IR-guided drainage. The mortality rate is 1-4%.

References:
1. Bickels,J., Ben-sira,L., Kessler,A.; Primary Pyomyositis; J Bone Joint Surg [Am];2002;84(12):2277-86.
2. Crum-Cianflone,N.; Bacterial, Fungal, Parasitic, and Viral Myositis; Clinical Microbiology Reviews;2008;21(3):473-94.
3. Karamazyn,B., Loder,R., Kleiman,M.; The role of pelvic magnetic resonance in evaluating nonhip sources of infection in children with acute nontraumatic hip pain; J Pediatr Orthop;2007;27(2):158-64.
4. Koudela,K.; Koudela,K., Koudeloya,J.; Secondary pyomyositis of hip muscles (non-tropical pyomyositis); Acta Chir Orthop Traumatol Cech;2008;75(3):196-204.
5. Lo,B., Fickenscher,B.; Primary pyomyositis caused by ca-MRSA; Int J Emerg Med;2008;1:331-2.
6. Mitsionis,G., Manoudis,G., Lykissas,M.; Pyomyositis in children: early diagnosis and treatment; J Pediatric Surgery;2009;44(11):2173-8.
7. Moran,G., Duran,C., Albinana,J.; Imaging on pelvic pyomyositis in children related to pathogenesis; J Child Orthop;2009;3:479-84.
8. Pannaraj,P., Hultren,K., Gonzalez,B.; Infective pyomyositis and myositis in children in the era of community-acquired methicillin-resistant Staphylococcus aureus infection; Clin Infect Dis;2006;43(8):953-60.
9. Peckett,W., Butler-Manuel,A., Apthorp,L.; Pyomyositis of the iliacus muscle in a child; J Bone Joint Surg [Br];2000;82(B):103-5.

Editor's Additional References:
10. Crum-Cianflone NF. Bacterial, fungal, parasitic, and viral myositis. Clin. Microbiol. Rev. 2008, 21(3):473.
11. Burdette SD, Watkins RR, Wong KK, Mathew SD, Martin DJ, Markert RJ. Staphylococcus aureus pyomyositis compared with non-Staphylococcus aureus pyomyositis. J Infect. 2012 Jan 13. [Epub ahead of print]

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