What are the suggested initial investigations for a patient concerned about temporalis muscle (temporal muscle) atrophy?

From the Guidelines

Initial investigations for a patient concerned about temporalis muscle atrophy should include electromyography (EMG) and a muscle biopsy, as these tests can help differentiate between inflammatory and noninflammatory myopathies and confirm a diagnosis. When evaluating a patient with temporalis muscle atrophy, it is essential to consider various differential diagnoses, including muscular dystrophy, mitochondrial myopathies, and noninflammatory myopathies 1.

Key Considerations

• A comprehensive history and physical examination are crucial in identifying systemic conditions that might cause muscle wasting.
• Laboratory tests such as complete blood count, comprehensive metabolic panel, erythrocyte sedimentation rate, C-reactive protein, creatine kinase, and thyroid function tests can help identify underlying conditions.
• Electromyography (EMG) should be performed to confirm a myopathic process and target a muscle for biopsy, as it can characterize polyphasic motor unit action potentials of short duration and low amplitude with increased insertional and spontaneous activity with fibrillation potentials, sharp waves, or repetitive discharges 1.
• A muscle biopsy is one of the most important investigative tools for differentiating an inflammatory from a noninflammatory myopathy and for subclassification purposes, and it is the gold criterion for confirming a diagnosis of idiopathic inflammatory myopathy (IIM) 1.

Additional Tests

• Imaging studies such as MRI of the head and neck can evaluate the temporal muscle structure and surrounding tissues.
• Nutritional assessment, including albumin, prealbumin, and vitamin levels, should be performed as malnutrition can lead to muscle wasting.
• Autoimmune markers like ANA and rheumatoid factor may be indicated if autoimmune conditions are suspected. The investigation approach should be guided by the patient's age, associated symptoms, and risk factors, as temporalis muscle atrophy can result from local pathology, systemic disease, neurological disorders, or aging-related changes.

From the Research

Initial Investigations for Temporalis Muscle Atrophy

The suggested initial investigations for a patient concerned about temporalis muscle atrophy include:

• Evaluating muscle mass and function, with temporal muscle thickness (TMT) emerging as a potential biomarker for muscle wasting 2, 3, 4
• Assessing for underlying causes of muscle atrophy, such as sarcopenia, denervation, or systemic diseases like chronic obstructive pulmonary disorder, cancer-associated cachexia, diabetes, renal failure, cardiac failure, Cushing syndrome, sepsis, burns, and trauma 5
• Conducting simple tests, including:
  • Creatine kinase levels 6
  • Thyroid function tests 6
  • (25)OH vitamin D levels 6
• Considering further evaluation, such as:
  • Neurophysiological studies 6
  • Muscle imaging 6
  • Muscle biopsy 6
• Using imaging modalities like computed tomography (CT), magnetic resonance imaging (MRI), or ultrasonography to measure TMT 2, 3, 4

Diagnostic Utility of Temporal Muscle Thickness

Temporal muscle thickness has been shown to be a useful diagnostic tool for monitoring muscle wasting in neurocritical care 2 and as a surrogate marker for skeletal muscle mass and nutritional status 3, 4. The diagnostic utility of TMT is supported by its strong association with grip strength and muscle strength in healthy individuals and patients with neurological disorders 3.