Syndromes of the peripheral nervous system
The Peripheral Nervous System (PNS) contains: Motor fibers that arise from lower motor neurons (LMNs) Sensory fibers that carry information from receptors to the CNS Autonomic fibers
A lower motor neuron consists of: The anterior horn cell in the spinal cord (or motor cranial nerve nucleus) Its axon The peripheral nerve The neuromuscular junction When a peripheral nerve is damaged, the muscle loses its direct nerve supply
Definition
The peripheral nervous system (PNS) includes:
- Cranial nerves. Spinal nerves. Nerve roots. Plexuses. Peripheral nerves
Lesions produce lower motor neuron (LMN) signs and sensory disturbances.
General Features of Peripheral Nerve Lesions
1.Motor Symptoms: Muscle weakness or paralysis. Muscle atrophy. Fasciculations. Hypotonia (decreased tone)
2.Reflex Changes: Hyporeflexia or areflexia
3.Sensory Symptoms: Pain. Paresthesia (tingling, numbness). Sensory loss
4.Autonomic Symptoms: Sweating abnormalities. Trophic skin changes. Vasomotor disturbances
Radicular Syndrome (Radiculopathy)
Definition: Lesion of one or more spinal nerve roots.
Features: Sharp shooting radicular pain. Sensory loss in a dermatome. Weakness in corresponding myotomes. Reduced reflexes
Causes: Disc herniation. Spondylosis. Tumors
Plexus Syndrome (Plexopathy)
Definition: Lesion of the brachial or lumbosacral plexus.
Features
- Motor and sensory deficits involving several nerves
- More extensive than a single nerve lesion
Causes: Trauma. Tumors. Diabetes
Mononeuropathy
Definition: Damage to a single peripheral nerve.
Examples: Median nerve → Carpal tunnel syndrome. Ulnar nerve palsy. Radial nerve palsy. Peroneal nerve palsy
Features: Weakness and sensory loss in the distribution of one nerve
Polyneuropathy
Definition: Diffuse symmetrical involvement of multiple peripheral nerves.
Clinical Features: Distal symmetrical weakness. Distal sensory loss ("glove and stocking" pattern). Reduced or absent reflexes
Causes: Diabetes mellitus. Alcoholism. Vitamin B12 deficiency. Toxic and metabolic disorders
Guillain-Barré Syndrome (GBS)
Definition: Acute inflammatory demyelinating polyneuropathy.
Features: Ascending symmetrical weakness. Areflexia. Mild sensory symptoms. Possible respiratory failure
CSF: Albuminocytologic dissociation (↑ protein, normal cells)