Infectious Disease Compendium

Myositis

Diagnosis

Pain in a muscle, CPK may not be all that elevated.

Epidemiologic Risks

Depends on the organism, as a rule some sort of trauma is needed to develop pyomyositis (i.e. bacterial). For the iliopsoas abscess it may be as little as getting a groin pull; I often see the disease in heavy lifters and basketball players diving for loose balls (especially the 35 year old who still thinks he is 23). HIV and diabetes are risks for pyomyositis.

Microbiology

Pyomyositis: Staphylococcus aureus, Streptococcus pyogenes. E. coli in the neutropenic (PubMed).

Psoas abscess can have mixed gi flora as a result of a colon perforation, and both Mycobacterium tuberculosis and Coccidioides immitis can both track down the iliopsoas from spine involvement.

Gangrene can involve the muscle: Clostridium perfringens, Streptococcus pyogenes, mixed synergistic disease (streptococci plus anaerobes plus coliforms).

Aeromonas hydrophilia: after fresh water exposure or use of leeches. Really.

Rhabdomyolysis: Influenza, echovirus, coxsackie, Epstein-Barr, Legionella pneumophila, Trichinella spiralis, Sarcocystis.

Any disseminated / bacteremic illness will cause myalgias and a blip in the CPK's. S. aureus bacteremia in particular likes to present with multifocal severe muscle pain.

Empiric Therapy

Debride and drain. Initial treatment depends on the suspected cause.

- Group A Strep: penicillin PLUS clindamycin PLUS 1g/kg IVIG day one, 0.5 g/kg day 2 and 3.

- Mixed synergistic necrotizing myositis: (third generation cephalosporins PLUS metronidazole) OR carbapenems OR (quinolone PLUS metronidazole or clindamycin) OR penicillin/beta-lactamase inhibitors. ALL SELECTIONS +/- aminoglycosides if septic.

- S. aureus pyomyositis: nafcillin / oxacillin OR cefazolin OR vancomycin OR linezolid.

- Gas Gangrene: penicillin PLUS clindamycin PERHAPS PLUS metronidazole. DO NOT delay antibiotics and debridement for hyperbaric unless patient has concomitant bends.

- Staph aureus necrotizing myositis: vancomycin PLUS clindamycin PLUS 1g/kg IVIG day one, 0.5 g/kg day 2 and 3 (the data here is extrapolation from TSS and data to support its use in staphylococcal disease is weak ie anecdotes, and the plural of anecdote is? Anecdotes, not data. But you have to work with what you have).

Pearls

Rants