From the Guidelines
The workup of calf myositis should include a complete rheumatologic and neurologic history, blood testing to evaluate muscle inflammation, and consideration of electromyography (EMG), imaging (MRI), and/or biopsy on an individual basis when diagnosis is uncertain. The diagnostic work-up should prioritize assessing muscle damage and inflammation, with initial laboratory tests including creatine kinase (CK), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) 1. Additional tests such as troponin to evaluate myocardial involvement, lactate dehydrogenase (LDH), and aldolase can also be elevated in myositis.
Key Components of the Workup
- Complete rheumatologic and neurologic history regarding differential diagnosis
- Rheumatologic and neurologic examination, including muscle strength
- Examination of the skin for findings suggestive of dermatomyositis
- Blood testing to evaluate muscle inflammation, including CK, transaminases (AST, ALT), LDH, and aldolase
- Inflammatory markers (ESR and CRP)
- Consideration of EMG, imaging (MRI), and/or biopsy on an individual basis when diagnosis is uncertain
Importance of Recent Evidence
The most recent study 1 from 2018 provides the highest quality evidence for the workup of calf myositis, and its recommendations should be prioritized. While earlier studies 1 from 2013 provide some guidance, their evidence is less recent and therefore less relevant to current clinical practice.
Clinical Considerations
In clinical practice, it is essential to consider the potential for overlap with neurologic syndromes, such as myasthenia gravis, and to evaluate for preexisting conditions that can cause similar symptoms. Paraneoplastic autoantibody testing for myositis and neurologic conditions may also be necessary in some cases. By prioritizing the most recent and highest quality evidence, clinicians can ensure the best possible outcomes for patients with calf myositis in terms of morbidity, mortality, and quality of life.
From the Research
Diagnosis of Calf Myositis
- Calf myositis is defined as inflammation within skeletal muscle, and its diagnosis may require integrated analysis of imaging findings with clinical, laboratory, and pathology data 2.
- Magnetic Resonance Imaging (MRI) plays an important role in the diagnosis and evaluation of patients with suspected myositis, but many entities may have imaging features similar to those of myositis and can be considered myositis mimics 2.
- Muscle biopsy is indispensable for making a reliable diagnosis of myositis, and the use of MRI of skeletal muscles and detection of myositis-specific autoantibodies have become useful additions to the diagnostic repertoire 3.
Clinical Features and Laboratory Findings
- Acute benign calf myositis is a rare infection-associated syndrome presenting with calf pain, and it can be diagnosed on a clinical basis 4.
- Laboratory evidence of a viral infection is often evident in patients with benign acute childhood myositis, and serum creatine phosphokinase is uniformly increased 5.
- Creatine kinase ratio is often elevated in patients with sporadic acute benign calf myositis, with a ratio of ≥10 in 70% of cases 4.
Differential Diagnosis
- Focal myositis of the calf can be associated with S1 radiculopathy, and MRI can provide evidence of global hypertrophy and inflammatory signals affecting the whole of 1 or several muscle heads of the triceps 6.
- Benign acute childhood myositis should be considered among the main causes of sudden-onset gait abnormality in young children, and it can be differentiated from other conditions based on clinical and laboratory findings 5.
- Myositis can be caused by infections, toxins, and drugs, and its diagnosis requires a comprehensive approach that takes into account the patient's medical history, physical examination, and laboratory results 2, 3.