Polyneuropathy is a serious condition affecting multiple peripheral nerve fibers, primarily impacting distal nerves with symmetric burning sensations or loss of feeling. Understanding the key differences between axonal loss and demyelinating polyneuropathy is crucial for proper diagnosis and treatment.
This comprehensive guide explores the various causes, symptoms, and diagnostic approaches for polyneuropathy, with a particular focus on common triggers like diabetes and alcohol consumption.
In my latest medical education video, I break down the complex topic of polyneuropathy into easily digestible segments:
Understanding the Nervous System Structure
The body’s nervous system consists of two main components: the central nervous system (brain and spinal cord) and the peripheral nervous system, which connects the CNS to organs, limbs, and skin. Peripheral nerve fibers come in various sizes, including myelinated motor nerves, myelinated/unmyelinated sensory nerves, and typically unmyelinated autonomic nerves.
Patterns of Nerve Injury
Axonal Loss
This most common form of polyneuropathy involves damaged neurons sending weaker signals. It typically:
• Affects longer nerve fibers first
• Starts distally and progresses proximally
• Impacts sensory nerves before motor nerves
• Usually affects legs before hands
Demyelinating Injury
This pattern involves the loss of myelin sheath, resulting in slower signal transmission. It typically affects large nerve fibers first, presenting with weakness more than sensory changes.
Common Causes and Differential Diagnosis
The main causes of polyneuropathy include:
• Diabetes
• Alcoholism
• Chemotherapy
• Vitamin B12 deficiency
• HIV infection
• Guillain-Barré syndrome
• Chronic inflammatory demyelinating polyneuropathy
• Charcot-Marie-Tooth disease
Diagnostic Approach
The gold standard for diagnosis is nerve conduction studies, which can differentiate between axonal and demyelinating injuries. Additional blood tests and specific examinations may be necessary to determine the underlying cause.