Peripheral neuropathy is a term describing any disorder of the peripheral nerves, which carry information to and from the brain and spinal cord. One, (mononeuropathy), several (polyneuropathy) or all of the peripheral nerves may be affected, causing problems with sensation, movement or autonomic functions (the automatic regulation of basic body functions like blood pressure).
Peripheral nerves may be affected by a variety of factors, which lead to impaired function, called a neuropathy. The causes may be broadly grouped as follows:
- heavy metal exposure - lead, mercury, arsenic
- some chemotherapy agents
- Infectious conditions - some examples are
- tickbite fever
- Inflammatory or immune-related conditions, such as
- Guillain-Barre syndrome
- rheumatoid arthritis
- systemic lupus erythematosus
- Systemic or metabolic disorders, such as
- uraemia - kidney failure
- hypothyroidism - underactive thyroid gland
- vitamin deficiencies - especially B group vitamins
- Hereditary disorders
- Frederich's ataxia
- injury - from vibration-induced (work-related), stab wounds
- prolonged exposure to cold
- prolonged hypoxia
- pressure injury - from immobility, crutches or plaster casts
Peripheral nerves have three main functions:
- Peripheral sensory nerves carry information from the periphery to the central nervous system about factors such as pain, touch, temperature, etc.
- They also relay instructions from the brain and spinal cord to initiate, control and co-ordinate muscle movements. Motor nerves
- A third function of the nerves is to regulate basic (autonomic) functions, such as dilatation or constriction of blood vessels, bladder control and bowel movements. Autonomic nerves.
Neuropathy can affect all these three functions, to different degrees, giving a unique mix of symptoms:
Sensory dysfunction may cause:
- Numbness, burning or tingling
- Inability to sense joint position - leads to poor co-ordination and clumsiness
Motor neuropathies generally cause loss of function:
- Lack of muscle control, poor co-ordination with fine movements
- Twitching and cramping of muscle groups
- Paralysis in later stages
- Wasting of muscles
- Difficulty breathing or swallowing in some cases
Autonomic problems may be widespread and include:
- Dizziness when standing (postural hypotension)
- Heat intolerance - inability to regulate body temperature, decreased sweating
- Difficulty in urination or incontinence
- Impotence in men
- Diarrhoea or constipation - problems with bowel motility
- Blurred vision
- Nausea and vomiting after eating, bloating, feeling full after eating even small amounts of food.
Examination may demonstrate the patient's lack of sensation, muscle weakness or wasting, abnormal reflexes and lack of co-ordination. Signs of underlying disorders may be found, for example rheumatoid arthritis.
The patient's description of symptoms and the findings at examination are often enough to make a clinical diagnosis, but some tests are needed to verify the diagnosis and to detect any treatable underlying causes.
Blood tests to identify metabolic disorders (like diabetes, thyroid and kidney dysfunction) or infection are done. Antibody and substance screens will identify auto-immune disorders, vitamin deficiencies or toxins.
X-rays or scans may be appropriate in some cases.
Specific tests to investigate neuropathy include:
- Nerve conduction studies
- Electromyography - to determine muscle function
- Skin biopsy - skin is rich in small nerve endings
- Nerve biopsy - not very helpful, and very rarely performed
The first step is to treat any underlying condition identified on testing, such as diabetes or thyroid disease, and to restrict exposure to toxins (alcohol, mercury, etc.)
Pain management is crucial, though not always successful. Gabapentin gives good results, as do Tricyclic antidepressants. Other medications used with varying results include carbamazepine, phenytoin, baclofen and dextromethorphan. Pregabalin and duloxetine are used with some success, specifically for diabetic neuropathy. Tramadol, non-steroidal anti-inflammatories or even low dose narcotics may be needed for extreme episodes of pain.
Physical interventions are also important - such as:
- walking aids, braces,
- regular foot care ( trauma may go unnoticed and complications may develop because of lack of sensation of pain),
- adequate environmental lighting,
- education about regular changes of posture to prevent pressure sores,
- changing eating patterns to avoid discomfort,
- instruction on manual bladder emptying/catheterisation.
This depends largely on successful treatment of the underlying cause.
Toxin -related problems may recover (incompletely) over a long time in case of a single episode of exposure. Recurrent exposure will exacerbate the problem.
Diabetic polyneuropathy trends to worsen over time.
Inflammatory conditions vary widely, but often subside slowly over several weeks, with final recovery depending on how severe the initial illness was.
The course of hereditary or congenital disorders is generally one of slow but inevitable progression of symptoms.
Some measures can be taken to prevent the development or worsening of neuropathies:
- strict glucose control in diabetes
- adequate treatment of metabolic and systemic diseases
- avoiding known toxins
- moderate use of alcohol
- ensuring good nutrition - including vitamins
- awareness of environmental dangers, such as work-related potential trauma, avoiding pressure problems.
Dr. AG Hall