13. Disorders of the motor neurons, nerve roots and peripheral nerves

Disorders of the peripheral nerves and nerve roots are usually acquired, unlike muscular diseases, which are often hereditary. Disorders of the peripheral motor neuron can be classified based on anatomy, loss of function and pathophysiology. Acquired dysfunction can be caused by metabolic or vascular disorders, compression and inflammation. Anterior horn cell (motor neuron) disorders are purely motor syndromes. Amyotrophic lateral sclerosis (ALS) is the most familiar cause. Polyneuropathy is a common feature of a systemic disease such as diabetes, but can also be caused by medication (chemotherapy in particular). Inflammatory neuropathies cause mainly symmetrical loss of strength; they have an acute (Guillain-Barré syndrome) or chronic course (chronic inflammatory demyelinating polyneuropathy, CIDP) and often respond well to treatment. Local nerve problems cause asymmetrical dysfunction, and sometimes pain. Familiar causes of mononeuropathy are carpal tunnel syndrome and paresis of the foot extensors due to pressure on the peroneal nerve. More extensive local dysfunction can be caused by plexopathy.