PERIPHERAL NERVE DISORDERS

The peripheral nervous system consists of:

• Anterior horn cells

• Nerve roots

• Peripheral nerves

• Neuromuscular junction

Diseases of the peripheral nervous system typically produce a lower motor neuron pattern of weakness.

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Components of a Peripheral Nerve

• Motor fibers

• Sensory fibers

• Autonomic fibers

Involvement of all three is common in polyneuropathies.

The evaluation of neuropathy follows a pattern-based approach.

Key questions:

1. Distribution of weakness and sensory loss

2. Symmetry (symmetric vs asymmetric)

3. Motor vs sensory predominance

4. Presence of autonomic symptoms

5. Time course (acute, subacute, chronic)

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Common Presentations

• Stocking-glove sensory loss

• Distal weakness

• Loss of ankle reflexes

• Paresthesias and burning pain

Based on Distribution

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Mononeuropathy

• Single nerve involvement

• Example: median nerve palsy

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Mononeuritis Multiplex

• Multiple individual nerves affected

• Often asymmetric

• Seen in vasculitis, diabetes

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Polyneuropathy

• Symmetric involvement

• Distal > proximal

• Most common pattern

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Based on Fiber Type

Type                    | Clinical Features     
Motor                | Weakness, wasting      
Sensory            | Numbness, pain      
Autonomic      | Orthostatic hypotension 
 

Axonal Neuropathy

• Distal weakness

• Early muscle wasting

• Reduced amplitude on nerve conduction studies

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Common causes:

• Diabetes

• Toxins

• Nutritional deficiency

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Demyelinating Neuropathy

• Proximal and distal weakness

• Markedly slowed conduction velocity

• Minimal early wasting

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Common causes:

• Guillain–Barré syndrome

• CIDP

GBS is an acute inflammatory demyelinating polyneuropathy.

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Clinical Features

• Acute onset

• Ascending symmetrical weakness

• Areflexia

• Minimal sensory loss

• Autonomic instability

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Cranial Nerve Involvement

• Facial nerve palsy common

• Bulbar weakness may occur

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Complications

• Respiratory failure

• Cardiac arrhythmias

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Investigations

• CSF: albuminocytologic dissociation

• Nerve conduction studies: demyelination

CIDP is the chronic counterpart of GBS.

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Clinical Features

• Progressive weakness over >8 weeks

• Proximal and distal involvement

• Sensory loss common

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Response to Treatment

• Steroids

• IVIG

• Plasmapheresis

The most common cause of peripheral neuropathy worldwide.

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Types

• Distal symmetric polyneuropathy

• Autonomic neuropathy

• Mononeuropathy

• Amyotrophy

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Clinical Features

• Burning pain

• Numbness

• Loss of ankle reflexes

• Autonomic symptoms

Autonomic involvement leads to significant morbidity.

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Clinical Features

• Orthostatic hypotension

• Gastroparesis

• Erectile dysfunction

• Bladder dysfunction

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Common Causes

• Diabetes

• Amyloidosis

• GBS

• Parkinsonism

Anterior Horn Cell Disorders

• Motor neuron disease

• Poliomyelitis

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Clinical Features

• Pure motor involvement

• Fasciculations

• Muscle wasting

• Areflexia

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Motor Neuron Disease (Overview)

• Progressive degeneration of motor neurons

• Combination of UMN and LMN signs

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Differentiating Neuropathy, Myopathy and NMJ Disorders-

Feature                | Neuropathy     | Myopathy      | NMJ      
Weakness          | Distal                   | Proximal         | Fatigable 
Reflexes              | Reduced             | Preserved      | Preserved
Sensory loss     | Present               | Absent             | Absent 
 

1. Identify pattern

2. Determine fiber involvement

3. Assess time course

4. Correlate clinically

5. Guide investigations