A 76-year-old woman with history of non-small cell lung cancer status post chemoradiation five years ago presented with acute onset of diffuse muscle weakness and swelling in bilateral forearms and legs, with a “woody” texture on palpation but without fluctuance. BP and HR were normal, but she had recurrent fevers as high as 103 for the first ten days of hospitalization without leukocytosis. ESR and CRP were elevated at 58 mm/hr and 18.7 mg/dL, respectively, and CK was over 3046 U/L. Initial concern was paraneoplastic myositis, given history of malignancy. Infection was also on the differential given recurrent fevers, and broad-spectrum antibiotics were started, though discontinued after five days when multiple repeat cultures were negative and CT chest/abdomen/pelvis showed no abscess. Viral studies were negative, including HIV, influenza, hepatitis C, as were fungal studies.
Paraneoplastic panels were ordered to check for a battery of antibodies. Thigh MRI revealed significant edema but no abscess, and thigh muscle biopsy was obtained. While awaiting results, patient was empirically started on intravenous immunoglobulin (IVIG) and high-dose solumedrol, given high suspicion for paraneoplastic myositis. She received four days of IVIG and solumedrol, but due to transfusion reaction, IVIG was discontinued.
PET scan revealed diffuse hypermetabolic muscular activity consistent with myositis but no cancer recurrence, and paraneoplastic antibody panel returned negative. She continued to improve after the short course of IVIG and solumedrol, with fever resolution and reduced swelling of affected muscle groups, without further use of antibiotics. Pathology reported pyomyositis with no evidence of the culprit microorganism, slides depicting mixed inflammation with neutrophils and tissue necrosis (Figures 1 and 2). Viral infections can also cause pyomyositis; possibly her condition was caused by a self-limited viral infection. Patient was significantly deconditioned, requiring rehab, but otherwise the myositis had resolved and has not yet recurred.
Discussion:
Pyomyositis is typically a tropical disease, and usually affects the younger demographic. It is a purulent infection of skeletal muscle arising from hematogenous spread usually with abscess formation. Predisposing factors include immunodeficiency, trauma, injection drug use, concurrent infection, and malnutrition. Our patient had no typical risk factors; thus, the pathological diagnosis was unexpected. Pyomyositis is most often caused by staphylococcus and streptococcus, requiring prolonged antibiotics and sometimes abscess drainage. Since all her cultures were negative, antibiotics were administered only for a brief period without clinical improvement; presumably treatment with high-dose IVIG effectively eradicated the skeletal muscle infection through immunomodulatory effects.
Conclusions:
As pyomyositis is still rare in temperate climates and early presenting signs and symptoms may be nonspecific, it is often not included in the differential diagnosis until the patient fails to respond to treatment for another diagnosis; mortality is as high as 10%.
Despite our high clinical suspicion of paraneoplastic myositis in this case, the diagnosis of pyomyositis should be considered in all patients presenting with a swollen, tender muscle, as rapid diagnosis and treatment often leads to complete resolution, while failure to recognize the condition can be fatal.