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At the top of any UK/US list of causes must be diabetes and alcohol, worldwide think leprosy

About

• Also see Length Dependent Polyneuropathy for more information
• Disease of the peripheral nerves which is a manifestation of many primary neurological diseases and systemic diseases
• Many different clinical patterns - patchy or symmetrical, distal or proximal, motor or sensory or autonomic

Aetiology

• Peripheral nerves can be crudely divided into large myelinated ones and small unmyelinated ones.
• Smaller ones carry pain and temperature and autonomic
• Large ones carry motor and sensory (vibration and proprioception).

Clinical

• Distal symmetrical sensorimotor axonal neuropathy leads to altered sensation which can be reduced or unpleasant: terms used include paraesthesia, dysasthesia (unpleasant tingling), allodynia (painful to touch or stroke), hyperaesthesia when there is heightened sensitivity and lastly neuropathic pain. Hypoaesthesia can lead to a feeling of walking on cotton wool. Distal loss of pain and temperature and pain can lead to injuries. The distal proprioceptive loss will lead to an ataxic gait. The loss often starts distally and moves proximally in what has often termed a glove and stocking distribution. A positive Romberg's test may be seen with marked sensory ataxia and suggests large fibre disease affecting proprioception.
• Distal weakness which is lower motor neurone by definition and so there is loss of distal reflexes and over time progressing to even a dropped footnoted with a compensatory high steppage gait. Usually, the feet are affected significantly before the upper limb. In severe cases, the ascending disease can lead to weakness of the intercostal and diaphragm and require assisted ventilation as is seen with Guillain Barre syndrome most classically.
• Autonomic nerve involvement can give postural hypotension, bowel, bladder and erectile difficulties.
• Hereditary causes are often associated with long-standing deformities such as pes cavus and pes planus and clawing of the foot. Motor symptoms are commoner with hereditary causes. Sensory symptoms are more associated with the acquired disease.
• Nerve thickening e.g. ulnar nerve, the sural nerve may rarely be seen but has a list of memorable causes - leprosy, CIDP, Refsum's disease, amyloidosis, Charcot Marie tooth (Types I and III) and Hereditary neuropathy with pressure palsies

Rate of onset

• Days : GBS, Vasculitis
• Weeks : CIDP
• Months/Years: Diabetes, Alcohol

Differentiating clues

• Speed of onset
• Alcohol abuse or Diabetic
• Cranial nerves involved or autonomic
• Sensory or Motor predominates
• Sensory : Pain/Temp (small fibre) loss or Vibration/Proprioception (large fibre)
• Family history : CMT

First line Investigations

• FBC (anaemia ↑ MCV)
• ↑ ESR and CRP: Malignancy, Vasculitis
• ↑ GGT, LFT : Alcohol
• ↑ Urea or creatinine: uraemia ↑ Ca: Malignancy
• ↑ Glucose ↑ HBa1c : Diabetes
• ↓ B12 ↓ Folate, TFTS
• ANA, dsDNA, ENA : Vasculitis
• CXR : Sarcoid, Malignancy, TB, Churg-Strauss syndrome
• EMG and nerve conduction studies are often indicated in the evaluation of a patient with peripheral neuropathy. They confirm the presence of neuropathy and provide information as to the type of fibres involved (motor, sensory, or both), the pathophysiology (axonal loss versus demyelination) and a symmetric versus asymmetric or multifocal pattern of involvement.

Selective tests

• CSF : GBS, CIDP ↑ protein
• ↑ ACE - sarcoid
• ANCA : Vasculitis/Churg Strauss
• Hepatitis B and C serology
• Cryoglobulins
• Complement C3 and C4
• Lyme and HIV serology
• Genetic studies
• Anti GQ1b : Miller Fisher syndrome
• Anti GM1 : MMN + CB
• Anti MAG : IgM Paraproteinaemic neuropathy
• Nerve biopsy usually of the sural nerve. Used for difficult cases.

Management

• See under specific cause