From the Guidelines
Proximal myopathy is primarily caused by several conditions including inflammatory myopathies, endocrine disorders, metabolic disorders, drug-induced myopathies, and inherited myopathies. The most recent and highest quality study 1 suggests that statin-associated muscle symptoms, including myalgias and myopathy, are common side effects of statin therapy, with a frequency of 1% to 5% in randomized controlled trials and 5% to 10% in observational studies. The study also highlights the importance of evaluating musculoskeletal symptoms before initiating statin therapy and identifying predisposing factors for statin-associated muscle symptoms, such as age, female sex, low body mass index, and comorbidities.
Some of the key causes of proximal myopathy include:
- Inflammatory myopathies (polymyositis, dermatomyositis)
- Endocrine disorders (hypothyroidism, Cushing's syndrome, hyperparathyroidism)
- Metabolic disorders (vitamin D deficiency)
- Drug-induced myopathies (statins, glucocorticoids)
- Inherited myopathies (muscular dystrophies)
Diagnosis typically involves:
- Blood tests for muscle enzymes (CK, aldolase)
- Inflammatory markers
- Thyroid function
- Vitamin D levels
- Electromyography
- Muscle biopsy may be necessary for definitive diagnosis
Treatment depends on the underlying cause:
- Inflammatory myopathies respond to immunosuppressants like prednisone or methotrexate
- Endocrine causes require hormone replacement or normalization
- Vitamin D deficiency needs supplementation
- Medication-induced cases improve with drug discontinuation
- Physical therapy is beneficial across all causes to maintain muscle strength and function
The pathophysiology varies by cause, with inflammatory conditions involving immune-mediated muscle damage, endocrine disorders affecting muscle metabolism and protein synthesis, and toxic myopathies involving direct muscle fiber damage from medications or metabolic derangements, as noted in studies 1.
From the Research
Causes of Proximal Myopathy
The causes of proximal myopathy can be diverse and include:
- Drugs, such as statins, corticosteroids, and antimalarials 2, 3
- Alcohol and toxin exposure 2, 3
- Endocrine and metabolic disorders, including thyroid disease, osteomalacia, and adrenal dysfunction 2, 3
- Idiopathic inflammatory myopathies (IIM), such as polymyositis, dermatomyositis, and inclusion body myositis 2, 3, 4, 5, 6
- Hereditary myopathies, including limb girdle muscular dystrophies and facioscapulohumeral muscular dystrophy 3
- Malignancy and infections, such as HIV and SARS-CoV2 3
- Sarcoidosis, an inflammatory disease that can manifest as muscle weakness and myalgia 2, 3
Underlying Conditions
Proximal myopathy can be associated with various underlying conditions, including:
- Glycogen storage diseases, such as McArdle disease 3
- Lipid deposition myopathy, a class of hereditary metabolic myopathies 3
- Viral infections, such as dengue virus and influenza virus 3
- Autoimmune diseases, such as systemic lupus erythematosus and Sjögren's syndrome 3, 5, 6
Diagnostic Approach
The diagnostic approach to proximal myopathy should include:
- Clinical assessment to distinguish proximal myopathy from other conditions 2
- Simple tests, such as creatine kinase, thyroid function, and vitamin D levels 2
- Further evaluation, including neurophysiological studies, muscle imaging, and muscle biopsy, for patients with no toxic, metabolic, or endocrine cause 2
- Screening for malignancy and testing for anti-Jo1 antibody in selected patients with IIM 2, 5, 6