From the Guidelines
Proximal myopathy should be managed by addressing the underlying cause, which may include adjusting medications, supplementing vitamin D if deficient, or implementing specific therapies for autoimmune conditions, with a focus on maintaining muscle strength and function through physical therapy. This condition can be caused by various factors including autoimmune disorders, endocrine problems (especially thyroid disorders and Cushing's syndrome), certain medications (like statins and steroids), vitamin D deficiency, and inherited genetic disorders 1. Patients typically experience difficulty with activities that require these muscle groups, such as climbing stairs, rising from a seated position, or lifting objects above the head.
Key Considerations
- Diagnosis involves a thorough clinical examination, blood tests to check muscle enzymes (particularly creatine kinase), electromyography, and sometimes muscle biopsy 1.
- Treatment depends on the underlying cause, and may include pharmacological interventions, such as glucocorticoids, and physical therapy interventions involving the use of gentle exercise and activity, and management of the musculoskeletal system to prevent/minimise contracture and deformity 1.
- The prognosis varies widely depending on the underlying condition, with some causes being completely reversible when properly treated, while others may require ongoing management to prevent progression of muscle weakness.
Management Strategies
- Adjusting medications: discontinuing or modifying medications that may be contributing to proximal myopathy, such as statins 1.
- Supplementing vitamin D: ensuring adequate vitamin D levels to prevent deficiency-related muscle weakness 1.
- Implementing specific therapies: using immunosuppressants or other therapies to manage autoimmune conditions, such as polymyositis or immune-mediated necrotizing myopathy 1.
- Physical therapy: maintaining muscle strength and function through gentle exercise and activity, and managing the musculoskeletal system to prevent/minimise contracture and deformity 1.
From the FDA Drug Label
There have been rare reports of immune-mediated necrotizing myopathy (IMNM), an autoimmune myopathy, associated with statin use, including reports of recurrence when the same or a different statin was administered IMNM is characterized by proximal muscle weakness and elevated serum creatine kinase that persists despite discontinuation of statin treatment; positive anti-HMG CoA reductase antibody; muscle biopsy showing necrotizing myopathy; and improvement with immunosuppressive agents.
The FDA drug label associates proximal myopathy with immune-mediated necrotizing myopathy (IMNM), a rare condition that can occur with statin use, characterized by proximal muscle weakness and other specific criteria 2.
- Key characteristics of IMNM include:
- Proximal muscle weakness
- Elevated serum creatine kinase
- Positive anti-HMG CoA reductase antibody
- Muscle biopsy showing necrotizing myopathy
- Treatment may require discontinuation of statin therapy and the use of immunosuppressive agents.
In contrast, prednisone can cause acute myopathy, particularly with high doses, often in patients with disorders of neuromuscular transmission or those receiving concomitant therapy with neuromuscular blocking drugs 3.
From the Research
Definition and Presentation of Proximal Myopathy
- Proximal myopathy presents as symmetrical weakness of proximal upper and/or lower limbs 4
- It can also be described as generalized muscle weakness commonly involving the muscles of upper and/or lower limbs 5
Causes and Associated Conditions
- There is a broad range of underlying causes including drugs, alcohol, thyroid disease, osteomalacia, idiopathic inflammatory myopathies (IIM), hereditary myopathies, malignancy, infections, and sarcoidosis 4
- Toxins, long-term use of statins, corticosteroids, alcohol, SGLT2 inhibitors, COVID-19 vaccination, and antimalarials have been attributed to its development 5
- Endocrine and metabolic disorders, such as adrenal dysfunction, parathyroid and thyroid disorders, and pituitary gland disorders, can also contribute to this condition 5
- Idiopathic inflammatory myopathies, including polymyositis, dermatomyositis, inclusion body myositis (IBM), and Systemic Lupus Erythematosus (SLE), can cause moderate to severe muscle weakness 5
- Hereditary or congenital myopathies, such as limb girdle muscular dystrophies, facioscapulohumeral muscular dystrophy, Duchenne and Becker muscular dystrophy, and proximal myotonic myopathy, can also cause proximal myopathy 5
Diagnostic Approach
- Clinical assessment should aim to distinguish proximal myopathy from other conditions that can present similarly, identify patients who need prompt attention, and determine the underlying cause of myopathy 4
- Initial evaluation should include simple tests, such as creatine kinase, thyroid function, and (25)OH vitamin D levels 4
- Further evaluation, including neurophysiological studies, muscle imaging, and muscle biopsy, should be considered for patients in whom no toxic, metabolic, or endocrine cause is found, and in those with clinical features suggestive of inflammatory or hereditary myopathy 4
- Screening for malignancy and testing for anti-Jo1 antibody is indicated for selected patients with IIM 4
Management
- Management depends on the underlying cause and includes measures such as removal of the offending agent, correction of endocrine or metabolic problems, corticosteroids, and immunosuppressive therapy for IIM 4
- Physical therapy, rehabilitation, and genetic counseling for muscular dystrophies may also be necessary 4