Pain in a muscle, CPK may not be all that elevated.
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.
Aeromonas hydrophilia: after fresh water exposure or use of leeches. Really.
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.
Debride and drain. Initial treatment depends on the suspected cause.
- 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.
- 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).
Relevant links to my Medscape blog