Neuropathy

Question 1

What is polyneuropathy?

Answer 1

-A generalized disease of peripheral nerves [+/- cranial nerves]
=May be predominantly/only motor
=May be predominantly/only sensory
=May be mixed sensori-motor

Question 2

Pathophysiological processes of polyneuropathy

Answer 2

-Mainly demyelination (of peripheral NS)
-Mainly axonal

Question 3

Causes of polyneuropathy

Answer 3

-Genetic
-Toxic (alcohol, drugs, other toxins)
-Metabolic (DM, vitamin deficiencies)
-Auto-immune/Inflammatory (GBS)
-Paraneoplastic
-Infections (HIV, Leprosy)

Question 4

Predominately motor loss causes

Answer 4

-Guillain-Barre syndrome
-Porphyria
-Lead poisoning
-Hereditary sensorimotor neuropathies (HSMN) - Charcot-Marie-Tooth
-Chronic inflammatory demyelinating polyneuropathy (CIDP)
-Diphtheria

Question 5

Predominantly sensory loss causes

Answer 5

-Diabetes
-Uraemia
-Leprosy
-Alcoholism
-Vitamin B12 deficiency
-Amyloidosis

Question 6

Clinical picture of polyneuropathy

Answer 6

-Weakness (LMN character)- wasting, normal/reduced tone
-Sensory loss
-Reduced or absent tendon reflexes
=Distribution depends on cause

-Classical sensory polyneuropathy picture
[for example, related to DM]
=Glove and Stocking Pattern with Areflexia

Question 7

Investigations for polyneuropathy diagnosis

Answer 7

-Nerve conduction studies
=Demyelination= slowing
=Axonal= reduced amplitude

Question 8

Presentation of Guillian-Barre syndrome

Answer 8

Guillain-Barre syndrome describes an immune-mediated demyelination of the peripheral nervous system often triggered by an infection (classically Campylobacter jejuni).

-Back/leg pain (65% initial)
-Progressive, symmetrical, ascending weakness of limbs (4 weeks, legs affected first)
-Reflexes reduced or absent
-Mild distal paraesthesia

-History of gastroenteritis
-Respiratory muscle weakness
-Cranial nerve involvement (diplopia, bilateral facial palsy, oropharyngeal weakness)
-Autonomic (urinary retention, diarrhoea)
-Uncommonly papilloedema secondary to reduced CSF resorption

Question 9

Investigation of Guillian-Barre syndrome

Answer 9

-Immune-mediated demyelination of PNS triggered by infection
-LP (rise in protein with a normal white blood cell count)
-Nerve conduction: decreased motor nerve conduction velocity, prolonged distal motor latency, increased F wave latency, ganglioside GM1
-Contrast enhanced MRI spine

Question 10

Management of Guillian-Barre syndrome

Answer 10

IV immunoglobulin, plasma exchange, DVT prophylaxis

Question 11

Describe diabetic neuropathy

Answer 11

-Presentation: glove and stocking, burning/ shooting pain, numbness, paraesthesia, painless injuries, gastroparesis 2nd autonomic neuropathy. Lower legs first length of sensory neurons)

-Diagnosis: 10G monofilament for sensation, reduced/ absent ankle reflexes

-Management: pregabalin/ gabapentin/ duloxetine/ amitriptyline, tramadol as rescue therapy for exacerbations of neuropathic pain/ topical capsaicin for localised neuropathic pain.
=first-line treatment: amitriptyline, duloxetine, gabapentin or pregabalin
=if the first-line drug treatment does not work try one of the other 3 drugs
=tramadol may be used as ‘rescue therapy’ for exacerbations of neuropathic pain
=topical capsaicin may be used for localised neuropathic pain (e.g. post-herpetic neuralgia)
=pain management clinics may be useful in patients with resistant problems

Question 12

Gastrointestinal autonomic neuropathy

Answer 12

Gastroparesis
occurs secondary to autonomic neuropathy
symptoms include erratic blood glucose control, bloating and vomiting
management options include metoclopramide, domperidone or erythromycin (prokinetic agents)

Chronic diarrhoea
often occurs at night

Gastro-oesophageal reflux disease
caused by decreased lower oesophageal sphincter (LES) pressure

Question 13

Describe B12 deficiency

Answer 13

-Causes: pernicious anaemia, post gastrectomy, vegan diet, disorders of terminal ileum, metformin (rare)

-Presentation: megaloblastic anaemia, sore tongue and mouth, mood disturbances, joint position and vibration affected before distal parenthesis (dorsal column). Pernicious anaemia: lethargy, pallor, dyspnoea, mild jaundice, subacute combined degeneration of spinal cord.

-Investigation: blood test, low WCC and platelets, low vitamin B12, anti-intrinsic factor antibodies/ anti gastric parietal cell antibodies

-Management: 1 mg of IM hydroxocobalamin x3 for 2 weeks then once every 3 months, treat B12 first

Question 14

Describe subacute combined degeneration of the spinal cord

Answer 14

Subacute combined degeneration of the spinal cord is due to vitamin B12 deficiency resulting in impairment of the dorsal columns, lateral corticospinal tracts and spinocerebellar tracts..

Recreational nitrous oxide inhalation may also result in vitamin B12 deficiency → subacute combined degeneration of the spinal cord.

Features
-Dorsal column involvement
=Distal tingling/burning/sensory loss is symmetrical and tends to affect the legs more than the arms
=Impaired proprioception and vibration sense
-Lateral corticospinal tract involvement
=Muscle weakness, hyperreflexia, and spasticity
=Upper motor neuron signs typically develop in the legs first
=Brisk knee reflexes
=Absent ankle jerks
=Extensor plantars
-Spinocerebellar tract involvement
=Sensory ataxia → gait abnormalities
=Positive Romberg’s sign

Question 15

Describe folate deficiency

Answer 15

-Megaloblastic anaemia, neural tube defect.
-400mcg folic acid until 12th week of pregnancy/ at higher risk of neural tube defect= 5mg folic acid from before conception until 12th week of pregnancy.
-Treat B12 first to avoid precipitating subacute combined degeneration of cord.

Question 16

Describe thiamine deficiency

Answer 16

-Wernicke-Korsakoff syndrome (nystagmus, ophthalmoplegia- failure of lateral gaze, ataxia, amnesia, confabulation), heart failure (wet beriberi= dilated cardiomyopathy), dry beriberi (peripheral neuropathy).

-Investigation: erythrocyte thiamine pyrophosphate, ABG (raised anion gap metabolic acidosis), lactate (elevated), thyroid function tests (rule out thyrotoxicosis)

-Management: IV thiamine (hospitalised), magnesium, potassium, phosphate replacement, oral thiamine (community alcohol withdrawal)

Question 17

Describe alcoholic neuropathy

Answer 17

-Presentation: history of alcohol abuse, gait instability, paraesthesia in the distal lower extremities progressing proximally, paraesthesia of the fingers and hands appear once symptoms extend above ankle level, sensory symptoms typically present prior to motor symptoms

-Signs: loss of sensation and deep tendon reflexes in the lower extremities, sensory ataxia, positive Romberg’s sign; signs of alcoholic liver disease: ascites, splenomegaly, cutaneous telangiectasias, palmar erythema, finger clubbing, Dupuytren’s contractures. Reduced absorption of B vitamins

-Investigation: EMG and nerve conduction studies (axonal Sensori-motor peripheral neuropathy, LFTs

-Management: intervention, pain relief, vitamin supplement, physiotherapy

Question 18

Describe Charcot-Marie-Tooth disease

Answer 18

-MOTOR LOSS, abnormal gait due to foot drop, toe-walking as a child, paraesthesia minimal: length-dependent, symmetric glove and stocking distribution of abnormalities, distal muscle atrophy and weakness, inverted champagne bottle legs, frequently sprained ankles, hyporeflexia. High arched feet, hammer toes, stork leg deformity

-Investigation: EMG and nerve conducting studies (demyelinating, low nerve amplitude), genetic testing

-Management: physical and occupational therapy, bracing, orthopaedic surgery, exercise.

Question 19

Drug causes of neuropathy

Answer 19

-Amiodarone, isoniazid, vincristine, nitrofurantoin, metronidazole, colchicine, phenytoin, statins, thalidomide