Block 8 (Neuro) - L4, Flashcards
What is a neuropathy?
Broad term referring to a variety of syndromes in which 1+ nerves are affected by any of several known or unknown causes
What is a mononeuropathy?
Disorder of a single major named nerve
What are the two usual causes of mononeuropathy?
Trauma and compression
What is a polyneuropathy (or peripheral neuropathy)?
Disorder of multiple nerves, both major and small, unnamed nerves or branches
In the most common polyneuropathies, symptoms and signs are ___ and sensory loss or impairment occurs ___ and remains prominent.
Symmetrical; early
How does numbness and tingling present in peripheral neuropathy?
Distally in the toes and feet initially; later affect fingers and hands
Why are the longest nerves in the body affected first in peripheral neuropathy?
Their metabolic maintenance and axoplasmic flow are more susceptible to neurotoxic factors
Where are the sensory deficits found in peripheral neuropathy?
Stocking and glove pattern (hands and feet)
What are other symptoms seen in polyneuropathy?
- Paresthesia
- Dysesthesia
- Weakness/atrophy, beginning in the distal limbs
- Early loss or decrease of reflexes
- If autonomic nerves are involved - orthostatic hypotension, incontinence, impotence, sweating abnormalities
What is paresthesia?
Spontaneous tingling, “pins and needles” sensation
What is dysesthesia?
An unpleasant sensation from a non-noxious stimulus
What are the two basic pathological processes occurring in neuropathy?
- Demyelination
- Axonal degeneration
Note - one or the other tends to predominate or occur initially
What is the characteristic pathology seen in a mononeuropathy from focal compression?
Demyelination
What is carpal tunnel syndrome?
Mononeuropathy of the median nerve at the wrist; the flexor tendons passing through the carpal tunnel get inflamed and compress the median nerve. This presents with tingling and numbness of the hand, and thenar weakness or atrophy (only when severe).
How is carpal tunnel syndrome treated?
Local rest, splinting, anti-inflammatory medications, surgical decompression of the nerve
With a severe crush or penetrating focal nerve injury, axonal loss occurs via ___. What is this?
Wallerian degeneration - axons and myelin degenerate distal to the point of nerve injury.
Most polyneuropathies from toximetabolic causes have ___ as the primary pathology.
Axonal degeneration (demyelination is secondary/additional)
Most mononeuropathies are due to ___ or occur at typical sites of ___.
Trauma; nerve compression or entrapment
What are three common sites of nerve compression or entrapment?
- Median nerve at the wrist
- Ulnar nerve at the elbow
- Common peroneal nerve at the fibular head
What may cause a multiple mononeuropathy syndrome?
Systemic illness which is inflammatory/autoimmune (SLE), infiltrative (sarcoidosis), or infectious (leprosy)
What are some other causes of non-acute polyneuropathy?
- Medications
- Exposure to neurotoxins
- Social habits (alcohol use)
- Malnutrition and vitamin deficiencies
- Hereditary neuropathy (positive family history)
Hereditary neuropathy may cause limb weakness early in growth and development - what signs may develop as a result?
- Pes cavus (high-arched feet)
- Hammertoes
- Scoliosis
What EMG findings suggests demyelination vs. axonal loss in polyneuropathy?
- Primary slowing of nerve conduction velocity suggests demyelination
- Primary loss of amplitude suggests axonal loss
What can be used to confirm a diagnosis when the clinical picture or EMG suggests a chronic polyneuropathy due to inflammatory, immune-mediated, or vasculitic causes?
Sural (sensory nerve) biopsy
How is neuropathy treated?
Depends on the underlying cause - surgical decompression, optimal glycemic control (diabetic polyneuropathy), braces/splints/cane/waker, ankle-foot orthoses, topical capsaicin (substance P depleter), lidocaine patches, oral medications for neuropathic pain (anticonvulsants and antidepressants)
What is Guillain-Barre syndrome?
Rapidly progressive polyneuropathy that affects patients of all ages, most often following a recent viral illness (can also occur after surgery or trauma)
What happens in Guillain-Barre syndrome?
Immune system targets peripheral nerve myelin, which may have been modified by or antigenically similar to the virus encountered previously
How does Guillain-Barre typically present?
Ascending, areflexic paralysis; weakness may spread to the trunk, upper limbs, respiratory muscles, face, bulbar, and even extraocular muscles - this progression plateaus after 3-4 weeks
Sensory impairment is minimal (patient may report tingling or numbness)
How is Guillain-Barre diagnosed?
- EMG shows evidence of asymmetric demyelination in proximal and distal segments of various nerves
- Elevated CSF protein may be detected with few if any white blood cells and no signs of infection
How is Guillain-Barre treated?
- Hospitalize for observation since ventilation may be needed
- Plasmapheresis or IVIG
Mot patients recover fully
What is a common cause of polyneuropathies, mononeuropathies, autonomic neuropathies, and cranial neuropathies?
Diabetes mellitus
What are other causes of neuropathies?
- Metabolic or endocrine disorders (uremia, hypothryoidism)
- Rheumatologic disease (RA, SLE)
- Cancer or myeloma
- Infection (AIDS, leprosy)
- Nutritional deficiencies (B vitamins)
- Toxins (alcohol, lead, solvents, drugs)
What are myopathies?
Diseases of various causes where the primary pathology affects muscle directly
How do myopathies present, compared to neuropathies?
Most myopathies have proximal weakness or fatigue, normal sensation, and late loss of reflexes only after significant atrophy has occurred (neuropathies have distal limb weakness and early loss of reflexes)
Pain is not usually prominent, but may occur with muscle cramps or spasms during physical activity
What are some causes of myopathies?
- Severe influenza infection (viral-induced breakdown of muscle fibers)
- Medications (statins, corticosteroids)
- Endocrine disorders (Cushing’s, hypothyroidism)
- Hereditary condition involving glycogen or lipid metabolism
How are myopathies diagnosed?
- Measurement of serum CK
- EMG testing
- Muscle biopsy
What is polymyositis?
Inflammation of multiple muscles; in the US, it most commonly refers to an AI disorder affecting muscle, usually in adulthood
How does polymyositis present?
- Proximal weakness that evolves over weeks to months - difficulty climbing stairs, arising from a chair, holding up the head, raising the arms
- If dermatomyositis - rash involving the periorbital areas and knuckles
How is polymyositis diagnosed?
EMG testing
Muscle biopsy - inflammatory cell infiltrates amid necrotic and regenerating muscle fibers
What are muscular dystrophies?
Hereditary myopathies of variable progression and severity
What is Duchenne’s muscular dystrophy?
X-linked disorder due to a total deficiency of muscle dystrophin (structural protein)
What is the Gower’s maneuver?
Use of upper limbs when getting up off the floor; compensation for weak trunk and pelvic muscles
What other signs are seen in Duchenne’s?
Pseudohypertrophy of the calf muscles (replacement of muscle by fat and connective tissue)
What is myotonic dystrophy type I?
Autosomal dominant disorder caused by excessive trinucleotide DNA repeats on chromosome 19, which produces an abnormal protein kinase in muscle fibers; weakness affects the distal limbs, neck, face, and jaws; yotonia; cataracts, frontal baldness, infertility, cardiac arrhythmias
What is myotonia?
Peculiar impaired relaxation of a muscle after volitional contraction
What is a motor neuron disease?
Group of disorders where only upper motor neurons, lower motor neurons, or both are affected.
What is spinal muscular atrophy?
Group of disorders involving just anterior horn cells
What are the clinical findings of spinal muscular atrophy?
LMN signs - weakness, atrophy, fasciculation, loss of reflexes
What is Werdnig-Hoffman disease?
Infantile onset spinal muscular atrophy with fatal outcome due to respiratory weakness; patients have a bell-shaped thorax, frog-leg posture, and jug-handle upper limbs
What is primary lateral sclerosis?
Familial degeneration of the corticospinal tract in lateral columns of the spinal cord, not due to structural or metabolic lesions; presents with weakness, UMN signs
What is peudobulbar palsy?
Several disorders in which the corticobulbar tract is involved, causing facial weakness, impaired chewing, dysarthria, dysphagia, and hoarseness; jaw jerk is increased, while fasciculations and atrophy are absent despite significant weakness
What is the epidemiology of ALS (age, M vs. F)?
Begins at 40-70 years old, affects M>F
What are the pathological findings of ALS?
Degeneration of corticospinal and corticobulbar tracts, gliosis, and loss of anterior horn cells and pyramidal neurons
What can prolong survival by a few months in ALS?
Riulzole (glutamate antagonist working at the NMDA receptors)
