Neuro - Peripheral Neuropathy

Question 1

Peripheral Neuropathy

Pathophysiology
Clinical Features
Investigations

Answer 1

1. ) Pathophysiology - nerve damage that can cause pain, numbness or weakness,
   - axonal degeneration: most common, seen in systemic, metabolic, toxic, and nutritional disorders
   - segmental demyelination: primary destruction of the myelin sheath leaving the axon intact e.g. MS/GBS
   - both types can occur with each other
   - can also be categorised by the aetiology, type of nerve affected, nerve distribution, inheritance pattern
2. ) Clinical Features
   - sensory: burning, tingling, numbness, pain from a light touch/neuropathic pain, balance problems
   - motor: muscle weakness, cramping or twitching, abnormal reflexes, muscle wasting, foot drop
   - autonomic: constipation or diarrhoea worse at night, nausea, bloating, belching, early satiety, excessive sweating, orthostatic hypotension, impotence
   - peripheral polyneuropathy: symmetrical motor and/or sensory symptoms and signs in the four limbs
   - demyelinating neuropathy (e.g. GBS): weakness may be proximal and thus simulates myopathic disease
3. ) Investigations
   - bloods: FBC, U+Es, LFTs, HbA1c/BM vitB12, TFTs, heavy metals, CRP/ESR
   - raised gamma GT is seen in alcoholic neuropathy
   - electrophysiological studies: nerve conduction studies (NCS) and electromyography (EMG) can help differentiate axonal degeneration and demyelination
   - nerve biopsies: rarely needed

Question 2

Causes of Peripheral Neuropathy

Metabolic
Neurological
Cancer
Autoimmune/Inflammatory
Medications
Infection
Traumatic/Toxic
Other

Answer 2

1. ) Metabolic
   - diabetes, hypoglycaemia, hypothyroidism
   - vitamin deficiencies: B12, B6, B1, copper
   - liver and kidney failure, uraemia
   - excess alcohol and thiamine deficiency
   - severe systemic infection (sepsis)
2. ) Neurological
   - GBS, MS, Charcot-Marie-Tooth
3. ) Cancer
   - effect of tumours pressing on nerves
   - lymphoma, multiple myeloma
   - paraneoplastic sensory neuropathy
4. ) Autoimmune/Inflammatory
   - RA, SLE, vasculitis, Sjogren’s, coeliac’s
5. ) Medications
   - antibiotics: isoniazid, nitrofurantoin, metronidazole
   - phenytoin, amiodarone, thalidomide
   - some specific chemo drugs e.g. cisplatin(specific)
6. ) Infection
   - shingles, Lyme disease, diphtheria, botulism, HIV
7. ) Traumatic/Toxic
   - nerve damage in injury or surgery
   - lead, arsenic, mercury
8. ) Other
   - amyloidosis
   - idiopathic: 30% of peripheral neuropathy

Question 3

Neuropathic Pain

Clinical Features
Differential Diagnoses
Investigations
Management

Answer 3

1. ) Clinical Features
   - burning or tingling sensation
   - paraesthesia (pins and needles), electric shocks
   - loss of sensation to touch of the affected area
2. ) Differential Diagnoses
   - shingles: dermatomal postherpetic neuralgia
   - diabetic neuralgia: typically affects the feet
   - trigeminal neuralgia, multiple sclerosis
   - iatrogenic: nerve damage from surgery
   - complex regional pain syndrome (CRPS): abnormal nerve functioning often triggered by an injury, causes neuropathic pain isolated to one limb which can intermittently swell, change colour/temp, sweating
3. ) Investigations
   - investigate for peripheral neuropathy
   - DN4 Questionnaire: assess the characteristics of the pain and examination of the affected area, a score of 4/10 or more indicates neuropathic pain
4. ) Management - 4 first-line medications which should all be tried before moving on to other options
   - amitriptyline (TCA), duloxetine (SNRI antidepressant)
   - anticonvulsants: gabapentin and pregabalin
   - others options: tramadol (only for flares), capsaicin cream (localised areas), physio, psychological input
   - carbamazepine is first-line for trigeminal neuralgia

Question 4

Charcot-Marie-Tooth (CMT) Disease

Pathophysiology
Clinical Features
Management

Answer 4

1. ) Pathophysiology - an inherited (AD) disease of the peripheral motor and sensory nerves
   - causes dysfunction in the myelin or the axons
   - various types with different mutations/pathologies
   - sx onset before 10yrs but can be delayed until >40
2. ) Clinical Features
   - peripheral sensory loss, weakness in the hands and lower legs (particularly loss of ankle dorsiflexion)
   - reduced muscle tone, reduced tendon reflexes
   - ‘inverted champagne bottle legs’: distal wasting
   - high foot arches (pes cavus)
3. ) Management - no treatment, all supportive
   - OT/PT: assist with ADLs, maintain muscle strength
   - podiatrists to help with foot sx and suggest insoles
   - orthopaedic surgeons: fix disabling joint deformities