The cause of much inflammatory myopathy is unknown (idiopathic), and such cases are classified according to their symptoms and signs, electromyography, MRI, and laboratory findings.

The main classes of idiopathic inflammatory myopathy are polymyositis (PM), dermatomyositis (DM) (including juvenile, amyopathic, and sine-dermatitis form), inclusion-body myositis (IBM), immune-mediated necrotising myopathy (IMNM), and focal autoimmune myositis.

[2] If the criteria for PM are met but muscle weakness also affects the hands and feet or is not accompanied by pain IBM should be suspected, and confirmed when muscle cell biopsy reveals (i) cytoplasmic vacuoles fringed by basophilic granules and (ii) inflammatory infiltrate comprising mostly CD8 T lymphocytes and macrophages; and electron microscopy reveals filamentous inclusions in both cytoplasm and nucleus.

Patients with PM or DM almost always improve to some degree in response to treatment, at least initially, and many recover fully with maintenance therapy.

[5] To minimize side effects, patients on corticosteroids should follow a strict high-protein, low-carbohydrate, low-salt diet; and with long-term corticosteroid use a daily calcium supplement and weekly vitamin D supplement (and a weekly dose of Fosamax for postmenopausal women) should be considered.

[5] For patients not responding to this approach there is weak evidence supporting the use of intravenous immunoglobulin, ciclosporin, tacrolimus, mycophenolate mofetil and other agents; and trials of rituximab have indicated a potential therapeutic effect.

[7] Occupational and rehabilitation therapists can offer good advice on walking without falling and performing fine motor tasks, and can provide appropriate canes, braces and wheelchairs.

Speech pathologists can provide advice on preventing choking episodes and reducing the anxiety of an immanent aspiration for both patients and carers.