Chapter 12 - Evaluation of the Patient with Weakness
Questions
Define the following terms:
fatigue, rigidity, myopathy, neuromuscular junction/myoneural disease, upper motor neuron, lower motor neurons, polyneuropathy, Charcot-Marie Tooth, Lambert-Eaton myasthenic syndrome, paraneoplastic syndrome, myasthenia gravis, nerve conduction study, electromyography.Fatigue, from a neurologic perspective, means a decrease in the ability to exert force with repeated or sustained contractions of a muscle. This usually results from disease of the neuromuscular junction. However, laypeople almost never mean this when they use the term "fatigue."
Rigidity refers to a stiffness (increased muscle tone) that produced a smooth resistance to passive movement throughout the range of a passive movement. This is due to extrapyramidal disease, usually Parkinson disease.
Myopathy is a condition that damages muscles diffusely. These are either primary muscle disease or are secondary to some systemic problem. The primary diseases are due to familial (usually metabolic) disease, muscular dystrophies or inflammatory conditions of muscle. The secondary myopathies are usually toxic, endocrinological or infectious.
Neuromuscular junction (myoneural) disease is a condition
that is damaging the neuromuscular junction at the motor end-plate on muscles.
"Upper motor neuron" refers to the motor control neurons in the cerebral cortex and brain stem that give rise to descending pathways innervating motor neurons.
Lower motor neurons are the anterior horn cells and their axons that innervate muscle fibers. These axons traverse nerve roots, plexi and the peripheral nerves in their course to the myoneural junction.
Polyneuropathy is generalized damage to peripheral nerves. The
conditions that cause this are usually systemic (toxic, nutritional deficiency, autoimmune, endocrinolgic, metabolic, hereditary) and affect the longest nerve first. The symptoms are almost always seen in the feet first.
Charcot-Marie Tooth is a group of hereditary neuropathies
that usually begin to show clinical signs in late childhood and adolescence and
progress slowly. It notably affects muscles of the feet and calves early in the course.
Lambert-Eaton myasthenic syndrome is an autoimmune (and
often paraneoplastic) condition that produces weakness, usually of hip girdle muscles.
A paraneoplastic syndrome refers to remote effects of a
tumor. Most often it represents a condition in which antibodies directed at a
tumor damage other tissues of the body.
Myasthenia gravis is a conditon in which there is
antibody-mediated destruction of the acetylcholine receptors producing weakness
and fatigability of muscle.
A nerve conduction study is a test of speed and amplitude of
conduction of peripheral nerve fibers.
Electromyography is a needle study in which the electrical activity
of muscle fibers is recorded. It can detect damage to muscles and is sensitive
to muscle fibers that have been disconnected from their nerves (denervated).
12-1. What are the levels of the nervous system that can produce true weakness?
Answer 12-1. Upper motor neurons (descending tracts of the central nervous system); lower motor neurons (the anterior horn cell and the axons traveling through the peripheral nerve to the muscle); the neuromuscular junction; the muscle.
12-2. How is strength graded?
Answer 12-2. A 5 point scale, with 5 being normal, 4 being weak, 3 being only strong enough to move against gravity and no additional resistance, 2 being unable to move against gravity and 1 being a flicker of contraction of the muscle, but no actual limb movement of any kind.
12-3. How can strength be tested functionally?
Answer 12-3. The patient can attempt to hold the arms out in front, with weakness of the whole upper limb reflecting in pronator drift. Grip can be tested by squeezing of two of the examiner’s fingers. Making an “OK” sign with the thumb and index finger tests the thenar muscles. Abduction and adduction of the ulnar 4 digits tests interosseous and hypothenar muscles. Walking on the toes and heels, climbing a small step, hopping on one foot or rising from a chair tests lower extremity muscles.
12-4. Other than actual weakness, what other symptoms might the patient be describing when they use the term “weak”?
Answer 12-4. Most motor problems can be described as “weakness.” These include rigidity or incoordination (possibly due to extrapyramidal or cerebellar disease, respectively).
12-5. What is suggested by proximal, symmetrical distribution of weakness (hip and shoulder girdle)?
Answer 12-5. This is the pattern most often seen in a myopathic process.
12-6. What is suggested by distal, symmetrical distribution of weakness (feet and/or hands)?
Answer 12-6. This is the pattern most often seen in a neuropathic process.
12-7. What does it mean if there atrophy out of proportion to the degree of disuse?
Answer 12-7. This indicates lower motor neuron lesion.
12-8. What would be suggested by fatigability of muscles?
Answer 12-8. Neuromuscular diseases, such as myasthenia gravis, can produce fatigue of muscles. Remember, we are discussing the actual loss of strength with continued muscle contraction, not the symptoms that most patients call “fatigue.”
12-9. What conditions can cause transient weakness?
Answer 12-9. Transient ischemic attacks, neuromuscular diseases (like myasthenia), peripheral nerve entrapment problems, the periodic paralysis family of conditions or, rarely, migraine can cause transient weakness. Patients can also be transiently weak after a seizure (Todd paralysis).
12-10. What is suggested by a story of severe, global weakness associated with heavy meals or periods of exercise?
Answer 12-10. This is a story suggestive of one of the periodic paralyses (an ion channelopathy). There may be a family history of similar problems.
12-11. What systemic conditions can produce weakness?
Answer 12-11. Thyroid or adrenal dysfunction and certain rheumatologic/inflammatory conditions can lead to muscle damage (myopathy). Many systemic problems can lead to polyneuropathy (generalized damage to peripheral nerve). Also, diabetes mellitus, hypertension and dyslipidemas predispose to cerebrovascular disease, which can damage upper motor neurons.
12-12. How can pain affect the diagnosis of the patient with weakness?
Answer 12-12. Pain may be part of the condition (particularly those that damage nerves or muscle). Pain may also produce an unwillingness or even inability to use the body part.
12-13. What conditions can present as bilateral weakness of the lower limbs?
Answer 12-13. Myelopathy (damage or disease of the spinal cord) usually produces bilateral symptoms below a certain level, often with some bladder urgency (this may require urgent MRI scanning of the cord). Cauda equina compression (syndrome) is suggested by flaccid weakness of the legs, often with urinary retention or overflow incontinence. A progressive weakness of both legs, evolving over hours to days, is a presentation of Guillain-Barre syndrome (an acute demyelinating polyradiculoneuroapthy of an immune nature). Myopathic processes tend to affect the hip girdle muscles early and Lambert-Eaton myasthenic syndrome usually begins with proximal hip girdle muscle weakness.
12-14. What is the likely cause of weakness of one side of the body that is associated with a lower facial weakness on the same side?
Answer 12-14. The problem is with upper motor neurons above the level of the brainstem (usually cerebral cortex or internal capsule).
12-15. What is the likely cause of weakness of one side of the body that is associated with weakness on the opposite side of the head (tongue, jaw, palate or eyes)?
Answer 12-15. The damage is localized to the brain stem (usually the medial aspect).
12-16. What procedure can be used to objectively demonstrate whether nerves to a muscle are damaged?
Answer 12-16. EMG can determine whether lower motor neurons to a muscle are intact. The pattern of denervated muscles is then used to try to distinguish whether a single nerve is involved or whether this is due to damage to a nerve root or the nerve plexus.
12-17. What is the effect of upper motor neuron damage upon muscle bulk, tone, deep tendon reflexes and superficial reflexes?
Answer 12-17. Upper motor neuron damage generally produces increased deep tendon reflexes, along with diminished normal superficial reflexes and some pathological reflexes (such as Babinski)? Muscle tone is usually increased in a pattern of spasticity (clasp-knife).
12-18. What is the effect of lower motor neuron damage upon muscle bulk, tone, deep tendon reflexes and superficial reflexes?
Answer 12-18. Lower motor neuron damage generally produces decreased deep tendon reflexes in the effected area. Superficial reflexes are usually not effected unless the weakness is very severe. Muscle tone is usually decreased and there is often severe atrophy that develops over time. If the motor neuron itself is damaged, fasciculations are usually prominent.
12-19. What is the effect of muscle or neuromuscular disease on muscle bulk, tone, deep tendon reflexes and superficial reflexes?
Answer 12-19. Usually all of these are normal, although very late in muscular disease there may be atrophy.
12-20. What kinds of problems produce diffuse muscle damage (myopathy).
Answer 12-20. Problems with muscle include congenital/hereditary (muscular dystrophy, congenital myopathy),; infection (trichinosis); connective tissue disease (polymyositis, scleroderma, mixed connective tissue disorder); endocrine (hypo/hyperthyroid, hyperparathyroid, hypo/hyperadrenia); neoplastic; drug-induced (clofibrate, statins, corticosteroids).
12-21. What kinds of conditions damage or block the neuromuscular junction?
Answer 12-21. Problems with neuromuscular junction include: paraneoplastic (Lambert-Eaton Myasthenic syndrome); immunologic (Myasthenia gravis); toxins (botulism, snake venom, tick bite); drugs(antocholinesterase toxicity).
12-22. What differences would be expected between myasthenia gravis and Lambert-Eaton myasthenic syndrome (LEMS).
Answer 12-22. Myasthenia gravis causes progressive weakness during sustained or repeated contraction. This usually affects the eyes early (though it can primarily affect speech and swallowing or be generalized). LEMS patients usually get stronger with repetition. It tends to affect hip girdle muscles most prominently and tendon reflexes are usually diminished (and improve after exercise).
12-23. What is the effect of lower motor neuron damage upon muscle bulk, tone, deep tendon reflexes and superficial reflexes?
Answer 12-23. Lower motor neuron damage generally produces decreased deep tendon reflexes in the effected area. Superficial reflexes are usually not effected unless the weakness is very severe. Muscle tone is usually decreased and there is often severe atrophy that develops over time. If the motor neuron itself is damaged, fasciculations are usually prominent.
12-24. What disorders can damage peripheral nerves?
Answer 12-24. Problems with peripheral nerve include: trauma (including entrapment); toxins (lead, alcohol, several medicines); infections (diptheria, Lyme, HIV); Inflammatory (CIDP, Guillain-Barre); metabolic (diabetes, porphyria); vascular (autoimmune arteritis); nutritional (vitamin B1 or B12 deficit or pyridoxine toxicity); heredity (Charcot-Marie-Tooth disease, etc); neoplasm; abnormal proteins (amyloidosis).
12-25. What kinds of conditions damage nerve roots?
Answer 12-25. Problems with nerve root(s) include: intervertebral disk herniation; neoplasm; foraminal encroachment; radiation; toxins, chronic meningitis.
12-26. What kinds of conditions damage anterior horn cells?
Answer 12-26. Diseases directly damaging anterior horn cells include: infection (polio); spinal cord trauma; tumors; paraneoplastic; degenerative (ALS, progressive spinal muscular atrophy); disc (spondylotic myelopathy); radiation myelopathy; vascular.
12-27. What kinds of problems are associated with upper motor neuron damage?
Answer 12-27. Disorders associated with damage to upper motor neurons include: vascular (stroke/TIA, AVM); tumor; trauma; infection (transverse myelitis, HIV); demyelination (MS); degeneration (ALS, primary lateral sclerosis); congenital (cerebral palsy); toxic/anoxic; developmental (Chiari, spinal stenosis).