Neurosurgery notes/Spine/Spinal Degenerative Diseases/Cervical degenerative disease/Cervical Spondylotic Amyotrophy (CSA)

Cervical Spondylotic Amyotrophy (CSA)

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Cervical degenerative disease

Definition:

  • CSA is a rare form of cervical spondylosis characterized by muscle weakness and wasting in the upper limb without significant sensory loss or lower limb symptoms.
  • It is caused by selective damage to the ventral nerve roots or anterior horn cells of the cervical spinal cord.

Diagnostic Criteria:

  • Severe unilateral or bilateral upper limb weakness and muscle atrophy.
  • Minimal or no sensory deficits and absence of gait disturbance.
  • Cervical spine imaging showing spondylotic changes and cord or root compression.
  • Electromyography (EMG) showing anterior horn cell involvement or nerve root damage.

Pathophysiology:

  • Two major mechanisms: direct mechanical compression of ventral nerve roots or ischemic injury to anterior horn cells.
  • Proximal type affects muscles innervated by C5-C6 (e.g., deltoid, biceps).
  • Distal type affects C7-T1 related muscles (e.g., triceps, hand muscles).
  • Vascular insufficiency due to compression of anterior spinal artery also contributes.

Clinical Features:

  • Muscle wasting and weakness mainly in shoulder, arm, and hand muscles.
  • Hand grip weakness and finger drop in distal type.
  • Sensory symptoms typically absent or very mild.
  • No significant lower limb or pyramidal tract signs.
  • Occasionally, dropped head syndrome due to posterior neck muscle atrophy.
  • Subtypes
    • Proximal-type (involving the scapular muscles, deltoid and biceps)
    • Distal-type (involving the triceps and muscles of the forearm and hand)
    • Diffuse-type (involving features of both the distal- and proximal-type)

Investigations:

  • MRI and CT to identify cervical spondylotic changes and evaluate cord or root compression.
  • EMG and nerve conduction studies to evaluate motor neuron and root function.
  • Cervical MRI may show cord atrophy or T2 hyperintensity in anterior horn regions.
  • A high intensity "snake eye"-like appearance (SEA) on axial T2-weighted MR images
 
notion image
notion image

Management:

  • Conservative treatment:
    • Cervical immobilization, physical therapy, pain control.
    • For 4 months if there is further deterioration for surgical treatment
  • Surgical treatment:
    • Aim: surgical treatment can be useful to halt disease progression
    • Options (no evidence one is better than the other)
      • ACDF
      • Posterior laminoplasty
  • Early surgical intervention is associated with better motor recovery.
  • Proximal CSA generally has a better surgical outcome than distal CSA.

Natural History:

  • Symptom progression is usually limited to a few myotomes.
  • Initial progression followed by symptom stabilization for years.
  • Muscle strength may improve or remain stable, especially with treatment.

Differential Diagnosis:

  • Amyotrophic lateral sclerosis (ALS) / motor neuron disease.
      • Feature
      Cervical Spondylotic Amyotrophy (CSA)
      Amyotrophic Lateral Sclerosis (ALS)
      Underlying Cause
      A clinical syndrome secondary to cervical spondylosis, caused by selective injury to the ventral nerve root (VNR), the anterior horn (AH) of the spinal cord, or both.
      Progressive degeneration of motor neurons in the primary motor cortex, brainstem, and spinal cord, eventually leading to death.
      Disease Course
      Self-limited course, with symptoms generally stabilizing for years after an initial progressive phase.
      Conservative treatment for a few months allows monitoring for progression, which is less likely in CSA.
      Characterized by progressive degeneration.
      Sensory Deficits
      Characterized by upper limb muscle weakness and atrophy without sensory deficits.
      Exclusion of sensory deficit is often considered a mandatory finding.
      Not explicitly defined as absent in the provided context, but ALS is a motor neuron disease.
      Pyramidal Tract Signs
      Typically absent or clinically insignificant.
      ALS involves degeneration of motor neurons (upper and lower).
      Bulbar Involvement
      Uncommon.
      Common, presenting as involvement of bulbar muscles, atrophy or fasciculation of the tongue, dysarthria, and dysphagia.
      Neck Musculature
      Generally associated with drooping shoulders (due to involvement of scapular muscles in proximal-type CSA).
      Atrophy of the neck extensor muscles leading to drooped head has been reported.
      Atrophy of the neck musculature and drooping of the head and shoulders, often with paraspinal wasting, are important localizing signs.
      Thenar Atrophy
      Distal-type CSA involves atrophy of the muscles of the hand.
      Severe atrophy of the thenar muscles is a rare occurrence.
      Onset Age
      Generally affects patients between the ages of 40 and 70 years.
      Peak onset is typically between the ages of 50 and 75 years.
      Nerve conduction testing
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      ADM-to-APB CMAP amplitude ratio (Abductor Digiti Minimi to Abductor Pollicis Brevis)
      significantly lower among patients with distal-type CSA
      Significantly higher among patients
      Ulnar-to-median nerve ratio (CMAP)
      ㅤ
      ratio is higher for ALS than for CSA
      Paraspinal and Trapezius Muscles
      No abnormal findings at the level of thoracic paraspinals and lower limb muscles have been reported.
      Diffuse fasciculation potentials in the trapezius and paraspinal muscles are suggestive of ALS.
      Abnormal spontaneous electromyographic activity of paraspinal muscles, associated with three or more thoracic segments (T7 to T10), is present in ALS and not CSA.
      Repetitive Nerve Stimulation (RNS) of the Trapezius Muscle
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      Decreases in the CMAP with RNS of the trapezius muscles are useful for distinguishing CSA from ALS.
      The RNS test for the trapezius muscle has high specificity (100%) and sensitivity (78%) for ALS, but not for CSA
  • Hirayama disease
      • Feature
      Cervical Spondylotic Amyotrophy (CSA)
      Hirayama Disease (HD)
      Typical Onset Age
      Generally affects patients between the ages of 40 and 70 years (middle age and elderly individuals).
      Typically affects individuals between the ages of 15 and 25 years (juvenile onset).
      Sex Predilection
      No specific gender ratio
      Primarily affects males (20:1)
      Underlying Cause
      Secondary to cervical spondylosis.
      Defined as a benign motor neuron disease.
      Clinical Course
      Self-limited course, with symptoms typically stabilizing for years after an initial progressive phase.
      Defined as a benign motor neuron disease.
      Muscle Atrophy Pattern
      Distal-type involves atrophy of the triceps and muscles of the forearm and intrinsic muscles of the hand.
      Characterized by unilateral atrophy of the muscles of the forearm innervated by the ulnar nerve, as well as atrophy of the intrinsic muscles of the hand (including thenar, hypothenar, dorsal/palmar interossei, and extensor/flexor digitorum communis muscles).
      Specific Imaging
      A high intensity "snake eye"-like appearance (SEA) on axial T2-weighted MR images
      MR imaging in neck flexion
      Ulnar-to-Median CMAP Ratio
      Lower compared to healthy controls.
      Lower among patients with HD than CSA
      APB CMAP Amplitude
      CMAP amplitude of the APB (Abductor Pollicis Brevis) is lower among patients with distal-type CSA than those with HD (P = 0.004).
      Higher than those with distal-type CSA.
      ADM-to-APB CMAP Ratio
      Lower among patients with distal-type CSA compared to controls (P < 0.001).
      Significantly lower among patients with HD (P < 0.001).
      Long-term History
      Although rare, a case has been reported where a patient initially diagnosed with HD was diagnosed with CSA 20 years later.
      HD is generally classified as benign.
  • Parsonage-Turner syndrome
  • Peripheral nerve palsies (e.g., posterior interosseous nerve palsy).
  • Rotator cuff tear or other orthopedic causes of upper limb weakness.

Reference