Neuropathy, Myopathy, and Motor Neuron Disease Flashcards
Mononeuropathy refers to involvement of a single, major, named nerve, usually by what two general etiologies?
Trauma; compression
Methods to localize mononeuropathy?
Beside neurological exam; EMG
Polyneuropathy (aka peripheral neuropathy) is a disorder of multiple nerves, but major and small, unnamed nerves, or branches. Describe the presentation of common polyneuropathies.
Symptoms and signs are symmetrical.
Sensory impairment occurs early and often remains prominent
Numbness and tingling begins distally, progresses to fingers and hands.
“Stocking and glove” pattern
May report paresthesia or dyesthesia
Early loss or decrease or reflexes
If autonomic involvement -> orthostatic hypotension, incontinence, impotence, sweating abnormalities
What are the two basic pathological processes at work in neuropathy?
- Demyelination
- Axonal degeneration
One or the other tends to predominate or occur initially
Demyelination is characteristic of what type of neuropathy
Mononeuropathy due to focal compression, such as carpal tunnel syndrome
Demyelination is also the primary process in what syndrome?
Guillain-Barre (acute type of polyneuropathy)
What happens in a severe crush or penetrating focal nerve injury?
Axonal loss via Wallerian degeneration, in which axons and myelin degenerate distal to the point of injury
Axonal degeneration is the primary pathology in what types of neuropathy?
Most polyneuropathies from toximetabolic causes
Most mononeuropathies are due to ___.
Trauma
Most mononeuropathies are due to trauma and occur at typical sites of nerve compression or entrapment, such as the ___ nerve at the wrist, ___ nerve at the elbow, and the ___ nerve at the fibular head.
Median; ulnar; common peroneal
List several general causes of multiple mononeuropathy syndromes.
Autoimmune (lupus)
Infiltrative (sarcoid)
Infectious (leprosy)
List some causes of non-acute polyneuropathy.
- Current or recent medications (eg, chemo)
- Toxic neuropathies (eg, neurotoxins in the workplace, alcohol, etc.)
- Malnutrition and vitamin deficiencies
- Hereditary neuropathy (+ family history, begins early in life)
If limb weakness occurs early during growth and development, what three physical exam findings may occur?
Pes cavus (high-arched feet)
Hammertoes
Scoliosis
When the clinical picture or EMG suggests a chronic polyneuropathy is due to inflammatory, immune-mediated, or vasculitic causes, what helps confirm the diagnosis?
Sural (sensory nerve) biopsy
If a non-acute polyneuropathy has no helpful historical clues as to its etiology, and the EMG test is non-specific, “screening” for a cause, particularly a treatable one, is done with what tests?
Blood tests for DM, liver or renal dysfunction, vitamin B12 deficiency, hypothyroidism, CBC to screen for anemia or other blood disorders
Rx significant median mononeuropathy at the rest?
May benefit from surgical decompression
Effective topical medications for neuropathic pain?
Topical capsaicin (substance P deplete) or lidocaine patches
Effective oral medications for neuropathic pain?
Anticonvulsants (gabapentin, pregabalin, carbamazepine)
Antidepressants (duloxetine, amitriptyline)
Presentation of GBS?
Rapidly progressive polyneuropathy
Any age
Follows a recent viral illness; may occur after surgery or trauma
Ascending, areflexic paralysis; progression plateus after 3-4 weeks
Signs of sensory impairment are minimal (patients may report tingling or numbness)
Pathogenesis of GBS?
Immune system targets peripheral nerve myelin, which was possibly modified by or antigenically resembles the virus encountered weeks earlier
Work-up of GBS?
Observation in an ICU, since MV may be needed
EMG shows evidence of asymmetrical demyelination in proximal and distal segments of various nerves
CSF: elevated protein with few if any WBCs and no signs of infection
Management of GBS?
Most patients recover fully; recovery may be hastened with plasmapheresis or infusion of IVIG
DM is a frequent etiology of polyneuropathy - what types of neuropathy may be seen?
Isolated or multiple mononeuropathies Autonomic neuropathies (gastroparesis or orthostatic hypotension) Cranial neuropathies (3rd nerve palsy)
In addition to DM, what are some other etiologies of polyneuropathy?
Metabolic/endocrine (uremia, hypothyroidism) Rheumatologic (RA, SLE) Cancer or myeloma Infection (AIDS, leprosy) Nutritional deficiencies (B vitamins) Toxins (alcohol, lead, solvents, drugs)
What are myopathies?
Several diseases of various causes where the primary pathology affects muscle directly
Presentation of myopathies?
Proximal weakness or fatigue
Normal sensation
Late loss of reflexes only after significant atrophy has occurred
Pain is not usually prominent
List some causes of myopathies.
- Severe influenza (viral-induced breakdown of muscle fibers, may cause rhabdomyolysis)
- Medications (statins, corticosteroids)
- Endocrine disorders (Cushing’s disease, hypothyroidism)
- Hereditary condition (glycogen or lipid metabolism)
Diagnostic testing for myopathy?
CK
EMG to confirm diagnosis and r/o other causes of weakness from neuropathy, myasthenia, motor neuron disease
Muscle biopsy in select patients
Presentation of polymyositis?
Autoimmune disorder affecting muscle
Usually affects adults
Proximal weakness evolving over weeks to months (difficulty climbing stairs, arising from a chair, holding up the head, raising the arms)
Presentation of dermatomyositis?
Muscle and skin involvement -> rash involving the periorbital areas and knuckles
Cause of Duchenne’s (X-linked) muscular dystrophy?
Total deficiency of muscle dystrophin (important structural protein)
Presentation of Duchenne’s?
Affects young boys
Trouble running, climbing, walking
Gower’s maneuver
Pseudohypertrophy (calf muscles replaced by fat and connective tissue)
Death occurs after weakening of respiratory muscles or from associated cardiomyopathy
Cause of myotonic dystrophy type 1?
Excessive trinucleotide DNA repeats on chromosome 19 -> abnormal protein kinase in muscle fibers
Autosomal dominant
Presentation of myotonic dystrophy type 1?
Weakness of the distal limbs, neck, face, and jaws -> mouth hangs open
Myotonia
Percussion of thenar muscles -> myotonia
Associated features: cataracts, frontal baldness, infertility, cardiac arrhythmias
Define myotonia.
Impaired relaxation of muscle after volitional contraction (eg, difficulty letting go of a handshake or doorknob)
What are motor neuron diseases?
Diverse group of disorders where only UMN, LMN, or both are affected
What are upper motor neurons?
Corticospinal tract and cotricobulbar tract that control the anterior horn cells and CN motor nuclei (LMNs)
Spinal muscular atrophy is a group of disorders involving just ___ cells.
Anterior horn
Presentation of spinal muscular atrophy?
LMN signs of weakness, atrophy, fasciculations, loss of reflexes
What is Werdnig-Hoffman disease?
Infantile onset spinal muscular atrophy with fatal outcome due to respiratory weakness
What is primary lateral sclerosis?
Familial degeneration of the corticospinal tract in the lateral columns of the spinal cord not due to structural (spinal stenosis from degenerative arthritis) or metabolic (B12 deficiency) lesions.
Presentation of primary lateral sclerosis?
Weakness, UMNs of spasticity, hyperreflexia, Babinski signs
What is pseudobulbar palsy?
Several disorders where only the corticobulbar tract is involved -> facial weakness, impaired chewing, dysarthria, dysphagia, hoarseness
Increased jaw jerk
Fasciculations and atrophy are absent despite significant weakness
Causes of pseudobulbar palsy?
Bilateral multiple cerebral infarctions Brain tumors Lesions of MS Brain trauma Rarely from a degenerative disorder
Presentation of amyotrophic lateral sclerosis?
Begins at 40-70 years of age, M>F
Initially focal weakness and atrophy in a limb with subsequent spread, progression to bilateral; others may have initial bulbar symptoms
Both UMN/LMNs degenerate -> widespread fasciculations, signs of each
Cause of familial ALS?
Defective superoxide dismutase enzyme -> destruction of motor neurons by free radicals
Pathological findings of ALS?
Degeneration of corticospinal and corticobulbar tracts, gliosis and loss of anterior horn cells and pyramidal neruons, and neurogenic atrophy of muscle
What can mimic ALS by causing LMN signs in the upper limbs and UMN signs in the lower limbs?
Cervical radiculomyelopathy from degenerative disc disease
What medication prolongs life in ALS? MOA?
Riluzole; opposes excitotoxic effect of glutamate at the NMDA receptors of motor neurons
