Myositis

Overview
Myositis is a general term for inflammation of the muscles. Many such conditions are considered likely to be caused by autoimmune conditions, rather than directly due to infection (although autoimmune conditions can be activated or exacerbated by infections.)

Elevation of creatine kinase (CK) in blood is indicative of myositis. The MM and not the MB or BB fraction of the CK will be elevated.

Differential diagnosis of myositis
Atorvastatin

Cellulitis

Deep vein thrombosis

Dermatomyositis

Hematoma

Idiopathic inflammatory myopathies

Inclusion body myositis

Influenza myositis

Juvenile dermatomyositis

Lovastatin

Lyme myositis

Myositis ossificans

Neuromuscular complications accompanying AIDS

Osteoarthritis

Osteomyelitis

Paraneoplastic neuropathy

Peripheral vascular disease

Polymyositis

Pravastatin (less likely than other statins)

Pyomyositis

Rheumatoid arthritis

Simvastatin

Statin therapy

Systemic lupus erythematosus

Toxoplasma myositis

Trichinosis

Trypanosomiasis

Tuberculous pyomyositis

Viral myositis (including following an episode of influenza)

Wasting syndrome

MRI
(Images courtesy of RadsWiki)