Peripheral nerve disorders

Question 1

Give differential for acute emergent weakness and possible respiratory compromise

Answer 1

Autoimmune

1) Demyelinating
- GBS
- Chronic inflammaotry demyeinating polyneuropathy
2) Myasthenia gravis

Toxic

1) botulism
2) buckthorn
3) seafood
- paralytic shellfish toxin
- tetrodotoxin (puffer fish, newts)
3) tick paralysis
4) Heavy metals
- Arsenic
- thallium

Metabolic 
-dyskalaemic syndromes
-hypophosphataemia 
-hypermagnesmia 
porphyria 

Infectious

• poliomyelitis
• Diptheria

Question 2

Describe guillian-barre

Answer 2

Pattern of symmetrical wekaness usually worse distally accompanied by variable sensory findings is characteristic of acute GBS

20% of patients remain disabled from this disease process and about 5% will die despite therapy

The most common form of GBS is an acute inflammatory demyelinating polyneuropathy representing 90% of the cases seen in the US

The most common infectious organism associated with GBS is Campylobacter jejuni
-CMV, EBC and mycoplasma pneumonia are also associated with subsequent development of GBS

Question 3

Describe the Miller Fisher Variant

Answer 3

Characterised by the triad of opthalmoplegia ataxia and areflexia.

Question 4

Describe the clinical features of GBS

Answer 4

Most patients seek treatment days to weeks after resolution of an URTI or GI illness presenting with progressive symmetrical distal (and usually to a less extent proximal) weakness.

Signs and symptoms are usually worse in the lower extremities annd are assoicated with diminution or loss of deep tendon reflexes, variable sensory finding and sparing of the anal sphincter. - The presence of distal parasethesia increases the liklihood of GBS as the diagnosis

Toungue weakness has been found to be associated with the development of respiratory compromise and the need for mechanical ventilation in patients with GBS-

Children have a signfiacintly higher rate of neuropathic pain associated with GBS (80%) but require mechanical ventilation much less componly (13%)

Question 5

Discuss Diagnosis of GBS

Answer 5

EMG
Nerve conduction studies
CSF –> marked elevated protein with only mild plepcytosis (albuminocytologic dissociation)
-normal CSF cannot be used to exclude GBS

Those with suspected GBS should ahve their respiratory function tested. A decrease in FVS correlates with the need for intuabtion.

Question 6

Discuss management of GBS

Answer 6

Patients with symmetrical weakness of relatively acute onset decreased or absent DTRs and variable degree of sensaory loss are managed as if they have GBS or one of its variants.

Definitive treatment are plasma exchange or IVIG
Combination or sequential therapy offers nil benefit over monotherapy
Plasma exchange is cumbersome and not avaiable in many hospital. IVIG is more readily avaibale and is usually administed ina dose of 400mg/kg/day for 5 days.

Steroids are not indicated and ahve been shown to delay recovery

Question 7

Discuss DDX of distal symmetrical polyneuropathy (DSPN)

Answer 7

Diabetes
alcoholism 
neopalstic or paraneopalstic 
Hereditary motor and sensory neuropathies (Charcot-Marie-Tooth) 
HIV
Tox

Question 8

Discuss DSPN

Answer 8

Most commonly seen in glove and stocking distribution with slow ascending progresssion.

The clinical picture of alcoholic polyneuropathy is similar to that of diabetes but is usually accompanied by severe myopathy and cerebellar degeneration

Question 9

Discuss management of DSPN

Answer 9

Mainstay is for stringent control of the offending agent.
If discomfort is severe and referral is likley to be dealyed initial pain management may be needed

NSAIDS are not first line due to poo efficacy and protentional for Renal impairment

TCA, anticonvulsants and SSRI and SNRI are useful treatment modalities
Pregabalin and gabapentin as adjuncts

Question 10

Discuss DDX of asymmetrical proximal and distal peripehral neuropathis

Answer 10

Brachial plexopathy

1) Open
- Direct plexus injury
- neurovascular (plexus ischaemia)
- iatrogenic (CVC)
2) CLosed
- Traction injuries (stingers, traction neuropraxia, partial or complete nerve root avulsion)
- Radiation
- neoplastic
- idiopathic brachial plexitis
- thoracic outlet

Lumbosacral

1) OPEN
2) Closed
- traction injures
- vasospastic
- neoplastic
- radiation
- infectious

Question 11

Discuss thoracic outlet syndrome

Answer 11

Describes a constellation of symptoms caused by compression of the neurovascular bundle at the thoracic outlet.
Manigestation include both neurogenic and vascular

Neurogenic
-Is caused by compression of the brachial plexus, presenting with upper extremity weakness, numbness paraesthesias and pain