From the Guidelines
A comprehensive myopathy lab panel should include muscle enzymes such as creatinine phosphokinase (CPK), LDH, AST, ALT, and aldolase, as well as a full blood count, ESR, CRP, and myositis-specific antibodies, as recommended by the consensus-based guidelines for the management of juvenile dermatomyositis 1. When evaluating a patient for myopathy, it is essential to consider a broad range of investigations to determine the underlying cause of the condition.
- The initial lab panel should include:
- Muscle enzymes: CPK, LDH, AST, ALT, and aldolase
- Full blood count and blood film
- ESR and CRP
- Myositis-specific and myositis-associated antibodies
- Additional tests may be necessary to rule out alternative systemic causes of myopathy, such as:
- Renal function and liver function tests
- Infection screen
- Investigations for endocrine disorders, electrolyte disturbances, and vitamin D deficiency
- Further tests for metabolic or mitochondrial myopathies, especially in the absence of cutaneous signs or atypical presentation
- Imaging studies, such as MRI of muscles and EMG, may also be crucial for definitive diagnosis, as recommended by the guidelines 1. The results of these tests should be interpreted in the context of the patient's clinical presentation, and a comprehensive evaluation should be performed to determine the underlying cause of the myopathy.
From the Research
Myopathy Lab Panel
The myopathy lab panel is used to diagnose and manage various types of myopathies. The following tests are commonly included in the panel:
- Creatine kinase (CK) levels: elevated CK levels can indicate muscle damage or disease 2, 3, 4, 5
- Thyroid function tests: to rule out thyroid disease as a cause of myopathy 2
- Vitamin D levels: to rule out vitamin D deficiency as a cause of myopathy 2
- Aldolase levels: elevated aldolase levels can indicate myopathy, especially in cases with normal CK levels 3, 4, 5
- Electromyography (EMG): to assess muscle function and detect abnormalities 3, 5
- Muscle biopsy: to examine muscle tissue for signs of disease or damage 2, 3, 5
- Autoantibody tests: to detect autoantibodies associated with idiopathic inflammatory myopathies (IIM) 6
Interpretation of Test Results
The interpretation of test results depends on the clinical context and the specific type of myopathy suspected. For example:
- Elevated CK levels can indicate muscle damage or disease, but may not always correlate with disease activity 6
- Elevated aldolase levels with normal CK levels can indicate a myopathy with perimysial pathology 4, 5
- The presence of autoantibodies can help diagnose and manage IIM, but disease-specific autoantibodies are only present in about half of patients with IIM 6
Additional Tests
Additional tests may be ordered depending on the specific type of myopathy suspected, such as: