Eight Flashcards
What are the 4 parts of a motor unit that can be damaged leading to disorders? What kinds of disorders does each lead to?
Anterior horn cell (motor neuron disorders), its axon (motor neuropathy-axons or myelin covering) and all muscle fibers (myopathy) innervated by it, including the neuromuscular junction (myasthenia gravis).
What are 4 sensory symptoms of motor unit disorders? What is each like?
- Paresthesiae are abnormal sensations described as tingling, prickling, pins and needles, warmth, cold or burning. Patients may also experience pain in the
dermatomal distribution. - Hyperesthesia or hypersensitivity is a phenomenon occasionally observed and probably represents a selective loss of larger sensory neurons which ordinarily exercise an inhibitory effect on the axons of smaller diameter neurons which, when removed, allow for over activity in the surviving smaller diameter axon, and leads to
unpleasant sensations. Mild stimuli may produce pain. - Hypesthesia means a loss of a sensory modality. Ordinarily, larger diameter modalities, such as position and vibratory sensation, are lost before intermediate diameter sensation, such as touch, which are in turn lost before small diameter modality, such as pain. In certain familial neuropathies, the order is reversed.
- Large-fiber sensory loss in the legs causes the gait to be wide based and ataxic. Ataxia is worse at night, as vision cannot compensate for the loss of position sense.. In the upper extremities, sensory loss may produce pseudoathetoid movements when the patients have their eyes closed.
What are 3 motor symptoms in motor unit disorders? When do they occur? How quickly?
Weakness occurs in the muscles innervated by the affected nerve. In total cessation of axonal function, the muscles are paralyzed.
Muscle atrophy can occur rapidly. Within one month after denervation, about 30% of muscle bulk is lost, within two months 60%, and within four months 80%. Muscle bulk then becomes stable.
Muscle hypertrophy
What are 6 possible autonomic changes in motor unit disorders?
Skin changes, Hair loss, impotence, constipation, diarrhea, gastric atony Urinary retention and overflow incontinence Postural hypotension
What is the general clinical manifestation of neuropathy, myopathy, motor neuron disorders, and neuromuscular junction disorders?
Neuropathy-Affects distally (starting in feet moving proximal, Deep tendon reflexes decreased, and sensory loss usually present
Myopathy-proximal distribution, decreased DTR,
NM Junction-Proximal, severe fatigue, normal DTR
Motor Neuron Disorder-assymmetric weakness, increased DTR
What is the most common presenting symptom of a neuromuscular disease? What does each number represent on the Medical Research Council Scale?
Weakness
MRC (Medical Research Council) Scale
5 - Normal motor strength
4 - Able to overcome gravity and some resistance
3 - Able to overcome gravity but no resistance
2 - Able to move a joint in full range of motion when gravity is eliminated
1 - Parts of muscle can contract but not able to move a joint
0 - No movement at all
What are 4 ways in which a good history can help make a diagnosis in NM disease?
a) Strength improving on exercise suggests Eaton-Lambert Syndrome
b) Strength worsens at the end of the day or after fatigue suggests myasthenia gravis
c) Muscle-strength worse on fasting suggests an abnormality of fat metabolism
d) Familial history suggests a dystrophy or congenital myopathy
What are 5 electrodiagnostic studies for NM disorders? How do they work? What are they used for?
ELECTRODIAGNOSTIC STUDIES
- Nerve Conduction Study: By stimulating the nerve electrically and recording over an appropriate muscle, conduction velocities are calculated. Demyelinating
lesions result in varying degrees of slowing due to interference with saltatory conduction; if severe enough the impulse may fail to pass the demyelinated
segment (conduction block). - Electromyography consists of placing a needle in different muscles and recording the electrical activities of the muscle. This can help to differentiate between
neuropathy and myopathy and extent of the lesion. - Repetitive Nerve Stimulation Studies involve rapid stimulation (8-9 stimuli) of nerves at low (2-5 Hz) and high (20-50 Hz) rates of stimulation to document
neuromuscular junction disorders. In myasthenia gravis decrement in the muscle action potential amplitudes is noted at 2-5 Hz while in Easton-Lambert syndrome > 100% increment is noted at 20-50 Hz of stimulation. - Muscle biopsy is a valuable diagnostic tool in myopathic and sometimes neurogenic process.
- Nerve biopsy: The sural or other distal sensory nerve may be taken for microscopic and electron microscopic study.
What are 3 classifications of nerve injury?
Neurapraxia-conduction block (compression)
Axonotmesis-Intact endoneurium, loss of continuity of axons
Neurotmesis-Loss of continuity of axons and endoneurium, possible loss of continuity of perineurium, and epineurium (complete loss of continuity)
What is acute compression ischemia like? What is chronic compression like?
Compression ischemia can be acute as in a period of lying on a nerve or having a constricting band placed about the extremity in which the nerve fibers may have a
transient conduction block or a more prolonged block due to focal demyelination.
Chronic compression, such as the ulnar nerve in telephone operators and shoe makers and the common peroneal nerve in tailors and oyster sorters produces demyelination and interneural proliferation of fibrous tissue and a slow deterioration of nerve function.
What is the most common compressive neuropathy? What is the most common etiology? What is the usual presentation? What other symptoms might occur with time? What are some possible therapies? Are there any other compressive neuropathies? Generally, How do they present?
Carpal Tunnel Syndrome is the most common compressive neuropathy. The etiologies are multiple and usually due to repetitive movements of the hand. The patient starts experiencing pain and numbness in the thumb, index and middle fingers. The patient may also have difficulty holding onto objects due to weakness of abductor pollicis brevis, opponens pollicis and flexor digitorum brevis. If the compression continues, the patient
may have axonal loss, which may lead to atrophy of the small muscles of the hand. The patients also develop Tinel’s sign, i.e., tingling while tapping over the flexor retinaculum. This sign is positive in only about 60% of the patients. The therapy includes splints, local steroid injections, and surgical release of the flexor retinaculum.
Compressive neuropathy of the ulnar nerve at the retrocondylar area, radial neuropathy at the radial groove, peroneal nerve at the fibular head and sciatic nerve at the sciatic notch could present with weakness and sensory symptoms at the distribution of the nerves.
What are some general symptoms of polyneuropathies?
Polyneuropathy is a syndrome characterized by symptoms of distal pain, paresthesia, weakness and neurological findings of distal, sensory and motor impairment and hyporeflexia. Autonomic dysfunction may be associated with some polyneuropathies. Acute, subacute, and chronic forms are described. Hyperesthesia and hypesthesia in a”glove stocking” pattern; never has a sharp margin nor does it encircle the limb like agarter.
What is the onset of acute polyneuropathies? What is the most common? What precedes it 1/3 of the time? by how long? What is noticed in CSF? What can diagnose it? What is the treatment? What causes the neuropathy?
Acute neuropathies have their onset over days or weeks. The most important syndrome is that of the Guillain-Barre. In about 1/3 of cases, an upper respiratory infection precedes the onset of a neuropathy by about two weeks. Spinal fluid protein is elevated in the majority of cases with few or no cells. Electrophysiological findings diagnose it. Supportive treatment; watch out for respiratory distress and autonomic dysfunctions. Give IVIG, plasma exchange. Manage pain—>Tricyclics, anticonvulsants, opiates/NSAIDS/etc. It is a demyelinating disorder.
What is the onset of subacute polyneuropathies? How common are they? What is the leading cause of them? What is its pattern? What happens in CSF? What are some other causes of subacute polyneuropathies?
Subacute polyneuropathies generally have their onset over weeks to months and comprise most cases of polyneuropathy. The leading cause in this group is diabetic polyneuropathy. Nerve dysfunction begins in the toes, moves up the leg. When it hits the knee, it will usually begin in the hand and move up. Less blood flow in these areas—>amputations. This ordinarily occurs in the known diabetic patient and is frequently associated with an elevated spinal fluid protein.
Nutritional, paraneoplastic.
What is the onset of chronic polyneuropathy? What is their etiology? Which is the most important example? How does it present?
Chronic polyneuropathy, having a time course extending over years, constitutes approximately 15% of the cases. The most common of these are the hereditary polyneuropathies, which include the entities of Charcot-Marie-Tooth.
Swelling of great auricular nerve, leg atrophy, hammertoes
