Types of neuropathy
Neuropathies are lesions affecting the nervous system and have a few distinctions and classifications, peripheral neuropathy refers to lesions affecting the peripheral nervous system. The lesion pattern can be affecting a single nerve at one site, a mononeuropathy, a single nerve at multiple sites, a mononeuropathy multiplex, or multiple nerves, a polyneuropathy.
These types of neuropathies have various primary causes based on lesion pattern.
As mononeuropathy is damage to a single nerve at a single site the cause is unlikely to be systemic, and are most often entrapment/compression, or trauma.
Mononeuropathy multiplex is often caused by inflammatory causes, and often vasculitis (inflammation of the vessels running in the nerve or by it.) The common vasculitis causes which can lead to mononeuropathy multiplex are, polyarteritis nodosa, systemic lupus erythematosis, and hypersensitivity vasculitis.
Polyneuropathies have diverse causes, and can be from:
- Immune mediated damage (e.g. Guillain-Barré Syndrome)
- Diabetes mellitus
- Toxins (e.g. CHemotherapy drugs)
- Nutritional deficiencies (e.g. vitamin B12)
- Inherited conditions. (e.g. Charcot-Marie-Tooth disease)
The type of damage also depends on the lesion pattern and some examples are
- Segmental demyelination
- Axonal degeneration
- Axonal degeneration followed by regeneration
Motor neuron diseases
These are diseases which cause damage to the upper or lower motor neurons in the CNS. We see different lesion patterns in each case, as detailed by matt bevin in this lecture. essentially lower motor neuron damage causes atrophy of muscle and no reflexes (reflexes bypass the upper CNS but LMN damage breaks the circuit). Upper motor neuron disease causes less atrophy and hyperreflexia as the UMNs no longer inhibit the strength of the reflexes.
Diseases and syndromes
Guillain-Barré Syndrome
This is also known as acute inflammatory demyelinating polyradiculoneuropathy. It is essentially an autoimmune disease which attacks the the myelination on the motor axons. It is usually reversible with partial or total function regained in 3-6 months with remyelination with supportive care.
What causes it
2/3 of cases are preceded by flu-like illness that resolves by the time the disease starts.
It is not very well known but there are known associations with certain viruses and bacteria. Some well known examples are
- Campylobacter jejuni
- Cytomegalovirus
- Epstein-Barr virus
- Mycoplasma
- HIV
How does it present
It presents as a creeping paralysis, distal to proximal, and can be fatal if the respiratory muscles are effected.
Morphology
The hallmark is inflammation of peripheral nerves, with infiltration by lymphocytes, macrophages, and plasma cells. The motor nerve cranial and spinal roots are most effected by the inflammation. Peripheral nerves undergo segmental demyelination.
Diabetic neuropathy
This is the most common neuropathy, with up to 50% of patients with diabetes having it. It is time related so after 15 yrs with diabetes 80% of patients have it.
What causes it
It is due to metabolic blood damage to nerves and tissue as well as ischaemic damage from thickening endoneural arterioles. Specific pathophysiology will come in the metabolism block module, which is not covered at time of writing finish
How does it present
This presents as symmetrical distal polyneuropathy with symptoms like numbness and lack of pain sensation.
Morphology
Any of these can occur:
- Axonal degeneration
- Demyelination
- Thickening of endoneurial arterioles
Charcot-Marie-Tooth disease
This is a hereditary syndrome causing dysfunction of the schwann cells causing myelination
Amyotrophic lateral sclerosis (generally laytermed motor neuron disease)
This is the most common motor neuron disease, and can affect both upper and lower motor neurons.
We can see effects associated with either LMN disease UMN disease or both.
end stage is failure of respiratory muscles, which is the cause of death in most patients.