Proximal Weakness 2018-01-30T16:37:17+00:00

Relevant physical signs

  • Inspection
    • Walking aids / wheelchair
    • Wasting of proximal muscles
    • Fasciculations (motor neurone disease)
    • Winging of the scapula
    • Ptosis (myasthenia gravis)
    • Hearing aid (sensorineural in 75% of facioscapulohumeral dystrophy, mitochondrial disease)
    • Facial droop (fascioscapulohumeral dystrophy)
    • Heliotrope rash / Gottron’s papules (dermatomyositis)
    • General habitus
      • Cushingoid appearance (Cushing’s syndrome)
      • Coarse facies, loss of outer third of eyebrow (hypothyroidism)
      • Prognathism, spade-like hands, large lips and nose (acromegaly)
    • Calf pseudohypertrophy (Duchenne / Becker muscular dystrophy)
  • Tone usually flaccid
  • Reflexes
    • Usually preserved in muscular dystrophies, inflammatory myositis, Cushing’s and Acromegaly
    • May be reduced in hypothyroidism
  • Power
    • Proximal weakness with relative sparing of extensors
    • May have weakness of facial muscles (especially eye closure) in FSH
    • Foot drop occurs late in FSH
    • If power is less than 4: no need to test coordination
    • Fatigability if myasthenia gravis suspected
  • Sensation
    • Spared in myopathies
    • If sensation involved, consider:
      • Co-existent peripheral neuropathy (especially if DM dermopathy is present)
      • Chronic inflammatory demyelinating polyneuropathy
      • Lead poisoning
  • Offer to do:
    • Beevor’s sign: upward movement of the umbilicus on contraction of abdominal muscles, due to relative weakness of lower abdominal muscles compared to upper abdominal muscles. Specific for facioscapulohumeral dystrophy.
    • Fundoscopy (retinitis pigmentosa, retinal telangiectasia in FSH)
    • Urine myoglobin (McArdle’s disease)

Differential diagnosis

  • Myopathies
    • Endocrine
      • Cushing’s syndrome
      • Hypothyroidism
      • Acromegaly
    • Inflammatory myositis
      • Polymyositis
      • Dermatomyositis
      • Systemic sclerosis
      • Mixed connective tissue disease
      • Anti-synthetase syndrome
    • Drug-induced
      • Statins
      • Alcohol
    • Metabolic
      • Glycogen storage disease (McArdle’s disease)
      • Mitochondrial myopathy
  • Neuromuscular junction
    • Myasthenia gravis
    • Lambert-Eaton myasthenic syndrome
  • Muscular dystrophies
    • Duchenne muscular dystrophy – X-lined recessive
    • Becker muscular dystrophy – X-linked recessive
    • Facioscapulohumeral muscular dystrophy – autosomal dominant in 80%, sporadic in the rest
    • Limb-girdle muscular dystrophy

Investigations

  • Electromyogram: early recruitment of a greater number of rapidly-firing motor units is the electrophysiological hallmark of myopathy
  • Elevated creatine kinase and aldolase point to muscle disease
  • Look for an underlying cause:
    • Endocrine myopathy: thyroid function tests, short synacthen test, IGF-1 levels
    • Inflammatory screen:
      • Anti-nuclear antibody
      • Extractible nuclear antigens such as anti-Jo1
    • Neuromuscular junction:
      • Nicotinic acetylcholine receptor antibodies or muscle specific kinase antibodies (MG)
      • Voltage-gated calcium channel antibodies (LEMS)

Management

  • Multidisciplinary team approach
  • Patient education
  • Speech, occupational and physiotherapy to maximize and preserve function
  • Treat the underlying cause, if any

Summary

Sir, this patient has proximal weakness. There is wasting of the proximal muscles, as well as pectoralis major. The scapula is winged, and there is also bilateral lower motor neurone facial weakness. Sensation is fully intact and the reflexes are normal. There is no ptosis and the weakness is not fatigable. There is no rash to suggest dermatomyositis.

Possible causes include a muscular dystrophy such as facioscapulohumeral dystrophy. Other causes of proximal myopathy include endocrine myopathies such as hypothyroidism, Cushing’s syndrome and acromegaly, inflammatory myopathies such as polymyositis, dermatomyositis and anti-synthetase syndrome, as well as drug-induced myopathies such as those caused by statins or alcohol.

Functionally, the patient requires the use of walking aids, and will likely require assistance with activities of daily living given that his power is 3/5.

Proximal Weakness

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