Motor neuropathy

Clinic

• Motor Neuropathy is an entity which occurs if the motor nerves which control muscle movements become damaged.
• As with sensory neuropathy, the parts of the body most likely to be affected are the feet, hands, legs and arms.
• It arises from disease processes affecting the motor axon and/or its surrounding myelin, however Lower motor neuron syndrome (LMNS) arises from a disease process affecting the spinal motor neuron itself.
• Motor neuropathy is a virtual entity which is made to define neuropathic disease
• Multifocal motor neuropathy is the classic disease which involve pure motor neuropathy.
• MMN is a almost a pure progressive motor neuropathy of extremities with Autoimmune Etiology.
• It is sometimes mistaken for ALS because of the similarity in the clinical picture, especially if muscle fasciculations are present

Sign / Symptoms

• Fasciculation / Twitching: Note that fasciculations or Twitching would be the used as an eliminated rubric
• Usually beginning in one or both hands and progress over long periods,
• Weakness / Muscle atrophy: Impaired balance and coordination
• Cramping: It usually involves very little pain, however, muscle Cramps/ Spasms / Twitches can cause pain.
• Profuse fasciculations (Twitching).
• Sensory nerves are usually unaffected
• Wrist / Foot drop a are common symptoms
• Gradual loss of finger extension
• Cold & hot temperatures exacerbate MMN symptoms to such an extent, unlike other neuropathies, that this temperature response is being investigated as a diagnostic tool.
• MMN is not fatal, however lead to significant disability

MMN vs ALS

• Unlike ALS, which affects both upper and lower motor neuron pathways, MMN involves only LMN pathway, specifically peripheral nerves emanating from the lower motor neurons.
• MMN can be difficult to distinguish from motor neuron disease since both present with Asymmetric, Progressive, Distal weakness without Numbness. Here is some distinguishing points
  1. MMN affects predominantly (but not exclusively) the upper limbs
  2. MMN usually lacks bulbar or respiratory involvement
  3. MMN is associated with less atrophy, unless it becomes severe or longstanding
  4. Cramps and fasciculations can occur in motor neuron disease but are less prominent than in MMN, occurring in up to 50% of patients with MMN
  5. MMN has no upper motor neuron signs
  6. The most important distinguishing feature of MMN is conduction block which is pathognomonic electrophysiological pattern of MMN.

Entities / Miasms

	PLV	JE	TBE	WNE
Asymmetric Paralysis Hemiparesis	+++	+++	+++	+++
Ext, Atrophy	+++	+++	+++	+++
Spasm	+++			+++
Fasciculation / Twitching	+++	+++	+++

Related disease

• Myasthenia gravis
• ALS, Motor Neuron Disease
• Upper motor neuron disease
• Sensory neuropathy