Clinical features of idiopathic inflammatory myopathies

Ashton, 2021Pipitone, 2020Schmidt, 2018Vencovsky, 2019

Adults, children and adolescents with idiopathic inflammatory myopathies usually present with subacute onset of nonselective symmetrical weakness in the proximal muscles (shoulder and hip girdle). People may also report myalgia and muscle tenderness. Dysphagia and dysarthria can occur, as can respiratory muscle weakness and myocarditis.

See the separate sections below for clinical features associated with specific inflammatory myopathies, including:

• dermatomyositis
• polymyositis
• necrotising autoimmune myopathy (NAM)
• overlap myositis
• myositis of antisynthetase syndrome
• inclusion body myositis (IBM).

Perform a complete physical examination including:

• testing muscle strength and function, to identify the pattern and severity of muscle weakness; a standard scoring system for muscle strength is outlined in The standard Medical Research Council scoring system for muscle strength
• a complete neurological examination
• a complete systemic examination (including skin and joints).

Proximal limb and neck flexor weakness are important findings that may support the diagnosis of an idiopathic inflammatory myopathyAshton, 2021.

Rarer causes of inflammatory myopathies to consider in the differential diagnosis may include:

• eosinophilic myositis, myofasciitis
• infection-related myositis
• granulomatous myositis, including sarcoid-associated myositis
• endocrine-associated myopathies (eg Graves disease, vitamin D deficiency)
• paraneoplastic syndromes.