Peripheral Neuropathy & Motorneurone Disease

These conditions can present with progressive weakness, often associated with muscle wasting and rippling movements of muscle (fasciculations). The hallmark of motorneurone disease is the virtual absence of sensory symptoms and additional involvement of the corticospinal tracts – it also tends to progress more rapidly than most neuropathies.

1. Peripheral Neuropathy

Peripheral nerves are the "wiring" in the arms and legs which course out from the spinal cord ending in the fingers and toes. Either the nerve ("wire") itself or its insulating sheath ("plastic coating") are affected by a number of different disease processes. The term peripheral neuropathy simply refers to an affliction of the peripheral nerves.

Symptoms may either be "motor" in which wasting and weakness of muscle predominate or "sensory" in which pain, numbness, tingling, cramps and spasms are more major features. Acute forms of peripheral neuropathy may be seen following chest and bowel infection and in autoimmune disease whereas more chronic forms occur in diabetes mellitus, cancer, some deficiency states and may follow exposure to the toxic effects of drugs (including alcohol) and poisons. They may also run in families.

Certain peripheral nerves are especially prone to trauma and pressure from entrapment. For example the median nerve is susceptible at the wrist and symptoms here are referred to as "carpal tunnel syndrome". Other vulnerable peripheral nerves include the ulnar nerve at the elbow, the common peroneal nerve at the knee, and the lateral cutaneous nerve of thigh at the groin (meralgia paraesthetica).

Confirmation of peripheral neuropathy relies on neurophysiology, and other testing includes bloods and chest x-ray. Occasionally in aggressive disease where initial testing has been unhelpful, it may be necessary to examine the spinal fluid at lumbar puncture and to biopsy a peripheral nerve, usually the sural nerve at the side of the foot. In 50% of cases, despite intensive investigation, no cause can be found and people with neuropathy need to be kept under careful review and reinvestigated from time to time. Treatment is that of the underlying disease.

2. Motorneurone Disease

This is a sinister progressive degenerative disease of spinal cord and brainstem which presents with either wasting or weakness of a hand, tripping on a leg or foot or problems with speech or swallowing.

Muscles may be either stiff or rippling/twitching (fasciculations) or both and people are often tired. Pain, depression and respiratory insufficiency occur as the disease marches on inexorably, with death occurring between three and five years from symptom onset. Sensation is not affected in any big way, and there are usually no problems with thinking, bowels, waterworks or sexual function.

In view of this disease's poor prognosis, extensive testing is necessary to exclude other potentially treatable disorders. Investigations might include MR Imaging, neurophysiology, spinal fluid examination at lumbar puncture, blood tests, respiratory function testing and occasionally biopsy of muscle.

No cause is known at the moment though some cases do tend to run in families. There is a single drug treatment, riluzole, which has been shown to slow disease progression and this is particularly useful where symptoms are detected early. Other management includes the use of many different symptomatic treatments, feeding via gastrostomy (PEG - Percutaneous Endoscopic Gastrostomy) and artificial ventilation usually using a non-invasive positive pressure technique, less commonly via a tracheostomy.