44. Polyneuropathies - classification, etiology, pathogenesis, clinical manifestations.

Polyneuropathies – classification, etiology, pathogenesis, and clinical manifestations

Polyneuropathy is a generalized, usually symmetrical disorder of peripheral nerves, affecting multiple nerves simultaneously, especially in distal limbs.

Classification

1. 1 According to type of nerve fibers involved

1. 2 According to pathology

1. 3 According to time course

Etiology (Causes)

Metabolic and endocrine

• Diabetes mellitus (most common worldwide).
• Uremia (chronic kidney disease).
• Hypothyroidism.
• Vitamin deficiencies (e.g., B1, B6, B12, E).

Toxic

• Alcohol (alcoholic neuropathy).
• Heavy metals (lead, arsenic, mercury).
• Drugs (e.g., chemotherapeutic agents like vincristine).

Infectious

• HIV.
• Leprosy.
• Lyme disease.
• Diphtheria.

Immune- mediated

• Guillain- Barré syndrome (acute inflammatory demyelinating polyneuropathy).
• Chronic inflammatory demyelinating polyneuropathy (CIDP).
• Vasculitic neuropathies (e.g., in systemic lupus, rheumatoid arthritis).

Hereditary

• Charcot- Marie-Tooth disease.

Pathogenesis

Axonal polyneuropathy

• Primary damage to axons, usually due to metabolic or toxic causes.
• "Dying-back" pattern: starts in longest nerves → distal sensory or motor loss ("stocking- glove" distribution).
• Leads to secondary myelin degeneration.

Demyelinating polyneuropathy

• Primary damage to myelin sheath → conduction slowing or block.
• Mainly immune- mediated (e.g., Guillain- Barré syndrome).
• Can also occur in hereditary demyelinating neuropathies.

Clinical manifestation

Sensory symptoms

• Distal symmetric numbness.
• Paresthesias ("pins and needles", burning, tingling).
• Loss of vibration and position sense (proprioception) → sensory ataxia.
• Painful neuropathies common in diabetes and alcohol- related cases.

Motor symptoms

• Distal weakness (foot drop, hand weakness).
• Muscle wasting in severe cases.
• Gait disturbances.

Autonomic symptoms

• Orthostatic hypotension (drop in BP when standing).
• Impotence.
• Bladder dysfunction (incomplete emptying).
• Abnormal sweating.
• Constipation or diarrhea.

Reflex changes

• Reduced or absent deep tendon reflexes (especially ankle reflex).

Distribution pattern

• Typically distal symmetric, starting in feet and moving proximally ("stocking- glove" pattern).