Peripheral neuropathy

Peripheral neuropathy causing respiratory failure can usually be identified clinically from the gradual evolution of ascending, or sometimes descending, weakness associated with paraesthesiae, sensory deficit, and reduced or absent tendon reflexes. Difficulties in diagnosis arise in rapidly evolving pure motor neuropathies, especially in the earliest stages when the tendon reflexes may be preserved. Also paraesthesiae occur in occasional cases of toxic neuromuscular conduction block, including botulism.10

Guillain-Barre syndrome is so much more common than any of the other causes of neuromuscular respiratory failure that there is a danger that other causes, including other causes of neuropathy, will be overlooked. The diagnosis of GBS cannot be made by any diagnostic test but requires the exclusion of other conditions (Table 11.1). The diagnosis of GBS itself is no longer sufficient since it is now recognised to be a syndrome with several underlying pathological processes.11 In Europe and North America over 90% of cases are due to acute inflammatory demyelinating polyradiculoneuropathy and the remainder to acute motor or motor and sensory axonal neuropathy.12 In northern China, Japan, India, and Central America the axonal forms of the disease are more common, accounting for up to 40% of cases. The distinction during life is difficult and depends on careful neurophysiological studies. In acute inflammatory demyelinating polyradiculoneuropathy there is multifocal partial conduction block or slowing of motor nerve conduction. In the axonal forms there is a reduction of compound muscle action potential amplitude with relative preservation of motor nerve conduction velocity.11-13 In very severe cases the action potentials may be unrecordable in which case the diagnosis can only be made by biopsy of an affected nerve. This is not worth performing except in a specialist centre.

The other causes of neuropathy (Table 11.1) can be ruled out by a careful history. Critical illness polyneuropathy occurs in the setting of an extremely ill patient who is being ventilated, has had sepsis and multiorgan failure, and cannot be weaned from the ventilator. It is due to an axonal neuropathy. The aetiology of critical illness polyneuropathy is not known but probably multifactorial.14 Careful enquiry about possible toxin exposure as a cause of polyneuropathy is always necessary. Acute ingestion of organophosphorus compounds is often due to attempted suicide and usually causes vomiting. After one to five days, as survivors emerge from coma, some develop acute paralysis with respiratory failure. This is called the "intermediate syndrome" to distinguish it from the later organophosphate induced delayed sensory and motor polyneuropathy which organophosphates may also cause. Electromyography shows pre- and postsynaptic impairment and the intermediate syndrome is probably due to necrosis of the neuromuscular junctions.15 The majority of patients with the intermediate syndrome recover spontaneously provided they do not suffer hypoxic brain injury. Inadequate pralidoxime therapy is proposed but not established as contributory. Poisoning with heavy metals severe enough to cause a neuropathy with respiratory failure has usually been preceded by an acute illness with vomiting and an altered level of consciousness often misdiagnosed as viral illness. Prominent cutaneous and muscular pain, especially in the soles of the feet, and preservation of the reflexes in the early stages should raise the suspicion of thallium poisoning.16 Painful tingling and weakness begin within one to five days from ingestion of thallium, before the characteristic hairfall. In arsenic poisoning, sensory symptoms such as pins and needles predominate early, and weakness may then develop.

Table 11.1 Peripheral neuropathies that cause respiratory failure

Condition

Specific test

Specific treatment

GBS (demyelinating from)

Nerve conduction block

IVIg PE

GBS (axonal form)

Small CMAPs

IVIg PE

Relatively normal MCV

CIDP

Nerve conduction block

IVIg PE S

Nerve biopsy

Critical illness

polyneuropathy14

Toxins

Organophosphorus

Red cell cholinesterase*

Atropine

compounds94

Blood OP

Pralidoxime

Urine OP

Thallium95

Dystrophic anagen hairs

with dark bands

95% sensitive and specific

for thallium poisoning

Whole blood thallium

Prussian blue

24 hour urine thallium

Arsenic1796-98

24 hour urine arsenic

Dimercaprol

Whole blood arsenicf

DMSA

Lead

Whole blood lead

Sodium calcium

edetate DMSA

Gold99

Dimercaprol

Lithium100101

Plasma lithium

Haemodialysis

Drugs:

Vincristine21102

Withdrawal

Lymphoma103

Nerve biopsy

Cytotoxics

Vasculitis: systemic

Nerve biopsy

S cyclophosphamide

lupus erythematosus104

IVIg?

Metabolic: acute

Urine porphobilinogen

Avoidance of

intermittent porphyria23

Urine d-ALA

precipitants

Intravenous haematin

Hereditary tyrosinaemia25

High calorie intake

Liver transplant

Diphtheria105

Throat swab culture

Antitoxin

Buckthorn neuropathy

(central America)20106

GBS = Guillain-Barre syndrome; PE = plasma exchange; IVIg = intravenous immunoglobulin; CIDP = chronic idiopathic demyelinating polyradiculoneuropathy; S = steroids; CMAPs = compound muscle action potentials; MCV = maximum conduction velocity; OP = organophosphorus d-ALA = d-aminolaevulinic acid; Prussian blue = potassium ferric hexacyanoferrate; DMSA = 2,3-dimercaptosuccinic acid.

*An isolated cholinesterase level may neither confirm nor exclude exposure because a normal cholinesterase level is based on population estimates. Ideally the diagnosis is based on a drop of 50% from baseline cholinesterase determinations. Animal studies have suggested in intermediate syndrome that AchE must be 20% or lower before muscle activity is affected. t An elevated arsenic level verifies the diagnosis whereas a low level does not exclude arsenic toxicity. Seafood ingestion may transiently increase arsenic levels too.

The early clinical picture sometimes closely resembles GBS and neurophysiological changes may initially show partial conduction block and slowing of conduction before giving way to changes suggestive of axonal degeneration.17

Diphtheria is now extremely rare in Europe and North America but cases were recently reported from Estonia18 and the diagnosis should be considered in patients with a recent upper respiratory infection, especially if there is prominent palatal involvement.19 Buckthorn neuropathy need only be suspected in those who have consumed berries from this bush in Mexico.20 Drugs usually cause an insidiously progressive distal axonopathy without respiratory involvement, but acute paralysis with respiratory failure occurred in a patient being treated with vincristine, possibly due to coincidental GBS.21 Both T and B cell lymphomas may cause acute neoplastic infiltration of the peripheral nervous system which can resemble GBS.22 Sometimes acute neuropathy is the presenting feature of the lymphoma. Vasculitic neuropathy rarely causes respiratory failure and usually only does so in the setting of a systemic illness with cutaneous, renal, and lung involvement. Acute neuropathy occurs in acute intermittent porphyria, usually after abdominal pain and vomiting, but sometimes as the presenting feature.23 It may be diagnosed during attacks by detecting increased urine porphobilinogen excretion, a test which should be considered in every case of undiagnosed acute neuromuscular paralysis.24 Recurrent neuropathy in infants is a feature of hereditary tyrosinaemia.25

Peripheral Neuropathy Natural Treatment Options

Peripheral Neuropathy Natural Treatment Options

This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.

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