How Can We Help?
Peripheral neuropathy
Overview
The long list of possible aetiologies makes these conditions somewhat daunting. Where resources are constrained, it is probably inappropriate to investigate simply for purposes of labelling, so a more pragmatic approach is to aim to identify all potentially treatable causes.
Motor neuropathies
- Guillain-Barre – characteristic presentation. If any doubt, CSF examination will show a mildly raised protein and no, or only a few, cells.
- Porphyria – sudden onset, associated abdominal pain, sensory signs often present as well.
- Rarely SLE and other vasculitides.
- Certain industrial chemicals such as lead, thallium and triorthocresyl phosphate – take a work history.
- Hepatitis, infectious mononucleosis, diphtheria.
- Diabetes may present with a predominantly motor neuropathy.
Predominantly sensory neuropathies
Usually present with discomfort in the feet; causes include:
- Nutritional deficiencies associated with alcohol abuse or malnutrition from other causes – e.g. beriberi.
- Medication adverse event – isoniazid probably the commonest.
- HIV- related polyneuropathy
- Diabetes
- Leprosy
- Associated with sepsis and chronic illness.
Approach to investigation:
- Go back and take a more careful history in all patients, including a family history and a drug history
- Do HIV, serum B12, CRP, TSH and serum glucose in all patients.
- An ANF and protein electrophoresis may be worthwhile.
- If leprosy is considered a valid possibility in your patient, then nerve biopsy is the appropriate diagnostic test.
- You should be able to identify a cause in more than 60% of patients.
- Even if no treatable cause is identified, do not neglect attention to education about foot care and prevention of injury.
Mixed motor and sensory neuropathies
Essentially the largest group. Apart from the sensory and motor neuropathies already mentioned, most of which can present also as a mixed picture, also consider mononeuritis multiplex secondary to vasculitides in the collagen-vascular diseases (PAN, RA, SLE especially), sarcoidosis, myeloma and carcinomas, amyloidosis and hypothyroidism.
Testing – same as for predominantly sensory neuropathy.
Who needs referral for an EMG?
Electrodiagnosis of nerve and muscle disease is laborious and time-consuming. Surface EMG is more attractive than needle EMG because it is less painful although the latter remains the gold standard. Lack of easy access to either facility should not be regarded as a major disability, as in most instances a reasonable clinical diagnosis can be reached by rational application of history, examination, and other investigations.
In general, lack of a clear diagnosis in a person with a potentially reversible neuromuscular disorder warrants discussion with a neurologist who may decide that an EMG will help with diagnosis, but as neurologist and EMG are usually in the same place, the distinction becomes academic.