Proximal Myopathy

Molecular advances of recent decades afford clinicians the capacity to diagnose myopathies through genetic testing. Initial clinical efforts aim to differentiate myopathy from other clinical scenarios by paying attention to the distribution of muscle weakness and patterns of involvement.¹

Barohn Recommendations: Six Key Questions

1. Which “negative” and/or “positive” symptoms does the patient demonstrate? (e.g. weakness vs. cramps and stiffness)
2. What is the temporal evolution? (episodic vs constant, with acute or sub-acute tempo)
3. Is there a family history of a myopathic disorder? (detailed family tree)
4. Are there precipitating factors that trigger episodic weakness or stiffness? (e.g. medications, exercise, fever, certain meals, etc.)
5. Are there associated systemic symptoms or signs? (e.g. other organ/tissue involvement, such as respiratory failure)
6. What is the distribution of weakness?¹

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The differential in a patient presenting with symmetrical weakness of proximal upper and/or lower limbs is broad:

Aetiology of proximal myopathy

1. endocrine
   1. thyrotoxicosis / myxoedema
   2. Cushing’s syndrome (especially iatrogenic)
   3. acromegaly
   4. osteomalacia
2. connective tissue disorders
   1. dermatomyositis
   2. polymyositis
3. hidden malignancy (paraneoplastic syndrome)
   1. e.g. carcinoma of lung
   2. carcinoma pelvis
4. alcohol
5. other drugs
   1. chloroquine
   2. steroids

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Assessing distribution of muscle weakness 

Manual muscle testing is important but for younger children observation of functional activity is sufficient. The following muscle groups should be tested, with specific patient positioning, where requisite, in parentheses.

• Upper Limb
  • shoulder: abduction; external and internal rotation
  • elbow: flexion, extension
  • wrist: flexion, extension
  • finger and thumb: extension, flexion, and abduction
• Lower Limb
  • hip: flexion (seated), extension, abduction (lateral decubitus)
  • knee: flexion (prone), extension (seated)
  • ankle: dorsiflexion, plantar flexion, inversion, eversion
  • toe: extension and flexion

If testing against gravity is not done, the presence of significant muscle weakness can escape recognition.¹

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References

1. Barohn, Richard J et al. “A pattern recognition approach to patients with a suspected myopathy.” Neurologic clinics vol. 32,3 (2014): 569-93, vii. doi:10.1016/j.ncl.2014.04.008.
2. Suresh E, Wimalaratna S. “Proximal myopathy: diagnostic approach and initial management.” Postgraduate Medical Journal 2013;89:470-477.
3. Gonzalez-Perez P, Torre M, Helgager J, et al. “Proximal muscle weakness.” Practical Neurology 2019;19:321-325.