Peripheral neuropathy

Peripheral polyneuropathy is a primary condition of the peripheral nerves causing symmetrical motor and / or sensory symptoms and signs in the four limbs.

There is a typical sensory change that is a symmetrical glove and stocking loss to all modalities. This pattern of sensory loss is unlike that of individual nerve or nerve root disease. In the latter cases the sensory loss is asymmetrical or confined to one limb.

In demyelinating peripheral neuropathies, such as Guillain Barre Syndrome, the weakness may be proximal and thus simulates myopathic disease.

It is important in the investigation of a peripheral neuropathy to be able to recognise the underlying pathological nature of the condition as it influences subsequent management (1)

• axonal degeneration is the most common pathology seen in systemic, metabolic, toxic, and nutritional disorders
  • characteristically has a predilection for large diameter and long fibres-distal axonopathy or dying back neuropathy
• segmental demyelination is primary destruction of the myelin sheath leaving the axon intact, although axonal degeneration may also be present in demyelinating neuropathies and secondary segmental demyelination may be seen in axonal degeneration
  • electrophysiological studies are helpful in differentiating primary demyelination from axonal degeneration
• neuronopathies are those conditions in which the cell bodies of axons-anterior horn cells or dorsal root ganglia are primarily affected

Generally, polyneuropathies can be categorized as (1,2):

• The aetiology
• The type of nerve affected (symptomatically)
  • Sensory
  • Motor
  • Autonomic
• The distribution of nerve injury
  • Distal
  • Proximal
• The part of the nerve being affected
  • Axonal degeneration
  • Demyelination
• The pattern of inheritance

Reference:

• McLeod JG. Investigation of peripheral neuropathy. Journal of Neurology, Neurosurgery, and Psychiatry 1995;58:274-283
• Gelb. D.J. (1995). Introduction to clinical neurology. Butterworth-Heinemann. p.158