9. Weakness

Question 1

A<span>lterations in plasma volume, electrolyte imbalance, anemia, decreased cardiac function, drop in systemic vascular resistance, increased metabolic demand (infection, toxin, endocrinopathy), and mitochondrial dysfunction (severe sepsis) can all produce non-localized weakness</span>

Question 2

<span>The differential diagnosis for generalized weakness is broad. Consideration of systemic causes such as infectious, neurological, toxicologic, metabolic, and physiological causes is important</span>

Question 3

<span>A detailed history should elucidate the nature, onset, and progression of symptoms, exacerbating or alleviating factors, and fluctuations in severity that may help discern if weakness is a result of cardiovascular disease, pulmonary insufficiency, metabolic disturbance, concurrent infection, toxic ingestion, medication imbalance, or malignancy. Medication reactions or interactions are an important consideration in patients taking multiple medications</span>

Answer 3

<span>A thorough review of systems should also be performed to identify associated signs or symptoms that may help to form a unifying diagnosis. </span>

Question 4

<span>Vital sign abnormalities, including bradycardia, tachycardia, tachypnea, fever, hypothermia, or hypotension should prompt immediate intervention and a search for a systemic cause of the weakness. </span>

Question 5

<span> Conditions involving UMNs tend to produce signs that include spasticity to extension in the upper extremities, spasticity to flexion in the lower extremities, hyperreflexia, pronator drift, and Hoffmann and Babinski signs. </span>

Question 6

<span>UMN signs signify a lesion within the cerebral cortex or corticospinal tract (CST) of the brainstem or spinal cord. Although these findings are not always detectable in the acute period, the presence of even one of them suggests pathology within the CNS. </span>

Question 7

<span>Weakness caused by LMN dysfunction is often accompanied by flaccidity, decreased reflexes, fasciculations, or muscle cramps. Lesions in the anterior horn of the spinal cord and its axonal extensions at the nerve root and peripheral nerve produce these findings.</span>

Question 8

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Answer 8

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Question 9

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Question 10

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Question 11

<span>Weakness involving the combination of arm, hand, or leg with ipsilateral facial involvement is generally caused by a lesio</span>

Answer 11

<span>contralateral cerebral cortex or the CSTs coursing down the corona radiata and forming the internal capsule</span>

Question 12

<span>Sudden onset of this weakness pattern often suggests hemorrhage or acute ischemia, whereas a gradual onset may be seen in demyelination (e.g., multiple sclerosis, acute demyelinating encephalomyelitis) or neoplasm</span>

Question 13

<span>Weakness involving the combination of arm, hand, or leg with contralateral facial involvement indicates a</span>

Answer 13

bstem lesion

Question 14

<span>The two main underlying processes that cause unilateral extremity weakness with contralateral facial involvement are</span>

Answer 14

vertebrobasilar insuff and demyelinating disease

Question 15

<span>Weakness involving the combination of arm, hand, or leg without facial involvement is most likely to be a result of one of the following three processes:</span>

Answer 15

<ul><li>•&nbsp;<div>A lesion in the medial, contralateral, cerebral homunculus (over the area where the lower extremity is represented)</div></li><li>•&nbsp;<div>A discrete internal capsule or brainstem lesion involving only the corticospinal rather than the corticobulbar tracts</div></li><li>•&nbsp;<div>Brown-Séquard internal capsule or brainstem lesion if the patient also has contralateral hemibody pain and temperature sensory disturbances below the level of motor weakness.</div></li></ul>

Question 16

<span>Isolated weakness of one extremity is usually caused by a</span>

Answer 16

sc or peripheral lesion

Question 17

<span>The examination for monomelic weakness presentations includes detailed strength testing and determination of whether weakness localizes to one ventral nerve root myotome or one particular peripheral nerve within the limb. Reflexes with a peripheral nerve disorder will be diminished, not hyperactive.</span>

Question 18

<span>Although radiculopathies can occasionally be purely motor, most peripheral lesions have some sensory component to their presentation; therefore, a careful sensory examination in the distribution of dorsal nerve root dermatomes and peripheral nerves is essential</span>

Question 19

Nonemergent causes of peripheral neuropathy

Answer 19

CTD<br></br>Ext compression - entrapm syndr, compressive plexopathy<br></br>endocrinopathy (db)<br></br>paraneoplastic syndromes<br></br>toxins (alc)<br></br>trauma<br></br>vit defic

Question 20

<span>NMJ disorders are considered when suspicion is low for a UMN source of isolated extremity weakness, reflexes are intact, and there are no sensory deficits to suggest a nerve or root problem. In such cases, the weakness is often mild, fluctuating, and worse later in the day. It usually involves the proximal arm or leg muscles, wrist extensors, finger extensors, or ankle dorsiflexors. NMJ disorder–induced weakness with only monomelic symptoms will be an uncommon diagnosis in the ED.</span>

Question 21

<span>When weakness involves the lower extremities only, the first consideration is a</span>

Answer 21

sc lesion

Question 22

<span>When weakness involves the lower extremities only, the first consideration is a spinal cord lesion. If this is the case, UMN signs may be absent in the acute period. Because the lateral spinothalamic tracts (LSTs) run in proximity to the CST, patients with bilateral lower extremity weakness frequently have alterations to their perception of pain or temperature. Examination may reveal a loss of pinprick sensation to a particular spinal level within the thoracic cord or terminal first lumbar segment. The lesion may be as high as T2 without producing upper extremity findings.</span>

Question 23

<span>The main causes of anterior cord syndrome are: 3</span>

Answer 23

ext compression<br></br>ischemia<br></br>demyelination

Question 24

Bilat weakness: <br></br><span>In the absence of UMN signs or a clear thoracic pinprick level, evaluation of perianal sensation, rectal tone, and urinary retention can identify deficits that point to cauda equina syndrome, compression of peripheral nerve roots running below the termination of the spinal cord</span>

Question 25

Bilat weakness: If the physical examination does not support a cord syndrome or cauda equina compression, the patient may have a peripheral neuropathy affecting the longest nerve tracts first. The acute presentation that is most concerning is Guillain-Barré syndrome (GBS). Rapid demyelination of peripheral nerves can result in symmetric weakness ascending from the feet. Sensory findings parallel the weakness, and reflexes should be decreased at some point in the patient’s clinical course. (1)

Question 26

When weakness involves the upper extremities only, the lesion is localized within the central portion of the cervical spinal cord where corticospinal fibers designated for hand and arm strength are located. The patient may have pinprick sensory loss over the upper extremities from the involvement of crossing sensory axons destined for the contralateral LST. However, light touch sensation, mediated by the posterior columns, should remain intact. Common causes of central cord syndrome include cervical spine hyperextension injuries and syringomyelia.

Question 27

When weakness involves all four extremities without facial involvement, the primary concern is a 

Answer 27

cervical spinal cord injury or process but pt first assessed for global weakness 

Question 28

One physical examination confounder in disorders that cause cord compression or ischemia is that upper extremity myotomes corresponding to the site of spine involvement will actually have LMN signs of flaccid weakness and decreased reflexes because anterior cells are involved at this particular level. However, UMN signs may be elicited below that level. A C5 lesion, for example, can cause diminished biceps reflexes but exaggerated triceps and patellar reflexes

Question 29

Weakness confined to the proximal portions of the upper extremities only points to a myofiber disorder, provided that there are no UMN signs or sensory deficits.

Answer 29

Patients may report general fatigue or trouble raising the arms above the head, climbing stairs, or rising from a chair. The common acute and progressive causes of proximal muscular weakness are inflammatory diseases such as polymyositis or dermatomyositis, or necrosis, as in rhabdomyolysis from 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors. 

Question 30

Myofiber m disorder:
Muscles are commonly but not always tender to palpation. Myositis patients can also have dysarthria and dysphagia from weakness of the pharyngeal muscles. Airway protective mechanisms may eventually be compromised.

Question 31

Weakness involving the distal portions of the extremities only is almost always caused by a peripheral neuropathy 

Question 32

Weakness involving the distal portions of the extremities only is almost always caused by a peripheral neuropathy (see Box 9.2 ). Patients will have weakness and poor coordination with fine movements of their feet or hands. If this type of distal weakness is present in both lower extremities only, the patient will most likely have a chronic peripheral neuropathy or an acute demyelinating neuropathy (GBS). The patient will also have some sensory disturbance over the feet. Examination for perianal sensory deficits or issues with fecal or urine continence will help exclude the compressive polyradiculopathy of cauda equina syndrome as a cause of bilateral distal lower extremity weakness. If only the fingers and hands are involved, evaluation for central cord syndrome is performed. Bilateral lower cervical radiculopathies or symmetrical polyneuropathies are possible but much less likely.

Question 33

Isolated, unilateral weakness of the upper and lower halves of the face is caused by a CN VII problem. Causes for an isolated CN VII neuropathy are Bell palsy, mastoiditis, and parotitis.

Question 34

Facial weakness not limited to CN VII will be associated with some combination of ptosis, binocular diplopia, dysarthria, or dysphagia. It can be caused by a brainstem lesion, multiple cranial neuropathies, or NMJ problem. 

Question 35

Dysfunction of one or more ocular, facial, or pharyngeal muscles will be the most common presentation for NMJ pathology. The history may indicate that the facial weakness is acute and progressive (botulism) or chronic and fluctuating (myasthenia gravis). Signs of these diseases can be determined by examining extraocular motion, facial expression, and soft palate rise. 

Question 36

Patients with an abnormality of the presynaptic release of acetylcholine (e.g., botulism, Eaton-Lambert syndrome, organophosphate poisoning) can have autonomic ganglia involvement and hence abnormal pupillary response to light, dry mouth, fluctuations in heart rate and blood pressure, anhidrosis, or gastrointestinal and bladder dysmotility.

Question 37

The management of neuromuscular weakness is based on evaluating the underlying cause and managing the acute complications of weakness. Airway protection in obtunded patients or those with upper airway compromise is paramount. Neck and pharyngeal muscle weakness, for example, may herald a risk for aspiration or airway obstruction. Diaphragmatic weakness and inadequate hypopharyngeal muscle control or respiratory muscle fatigue should prompt definitive airway protection by endotracheal intubation.

Question 38

Diaphragm weakness and inadequ hypophar m or resp m fatigue:
During rapid sequence intubation (RSI), succinylcholine should be avoided in suspected cases of progressive denervation of muscle of more than a 3-day duration due to receptor upregulation and the risk for severe hyperkalemia. In this situation, we recommend rocuronium, a nondepolarizing neuromuscular blocking agent.

Question 39

New quadriparesis or quadriplegia and hypotension without another cause is assumed to be caused by failure of autonomic sympathetic fibers in the cervical spinal cord. Consider a volume load and pressor support in addition to emergent imaging of this area. Although new weakness localizing to the spinal cord calls for immediate imaging, weakness from the spinal roots down does not always necessitate imaging in the ED unless cauda equina syndrome or other acute, emergent pathology is suspected

Question 40

Patients with suspected GBS need pulmonary function testing in addition to admission to a critical care setting for further management. An infectious or metabolic trigger is sought in patients with myasthenic crisis. If the patient is currently on acetylcholinesterase inhibitors, consideration should be given to a cholinergic crisis. Be aware of medications that may worsen weakness in patients with NMJ disease (e.g., aminoglycosides, quinolones, beta blockers).

Question 41

Rhabdomyolysis is treated with aggressive fluid resuscitation and intervention directed at the primary cause, if known.

Question 42

In any patient with a sudden onset of focal weakness, a vascular cause (occlusion or hemorrhage) should be strongly considered until excluded by an adequate imaging study. The presence of a severe headache with unilateral weakness, or midline back pain with lower extremity weakness, alerts the clinician to a compressive space-occupying lesion of the CNS or spinal cord, respectively.

Question 43

Laboratory tests are most useful for excluding non-neuromuscular causes of weakness (electrocardiography, measurement of hemoglobin, glucose, electrolytes, troponin, and lactate levels, urinalysis). Two exceptions are the creatinine kinase level in inflammatory myositis and potassium level in channelopathies.

Question 44

A 65-year-old man with a history of atrial fibrillation, on warfarin, with a supratherapeutic international normalized ratio (INR) of 4, presents with sudden onset right leg weakness and back pain. On examination, he is tachycardic to 108 beats/min and has 3/5 weakness to the right hip flexors and extensors, knee flexors and extensors, as well as ankle dorsiflexion and great toe extension. However, ankle plantar flexion is preserved. His knee reflexes are absent, but Achilles reflexes are normal. He has a normal Babinski reflex and no spasticity. He has sensory deficits throughout the anterior and posterior parts of his proximal leg as well as the anterior lower leg and dorsum of the foot. His posterior lower leg and plantar surface, however, have normal sensation. Rectal tone is normal, and there is no urinary retention. What is the most likely diagnosis?

• a. 
  Anterior cord syndrome from epidural hematoma
• b. 
  Cauda equina syndrome
• c. 
  Guillain-Barré syndrome
• d. 
  Hemorrhagic anterior cerebral artery (ACA) distribution stroke
• e. 
  Retroperitoneal hematoma with lumbar plexopathy

Answer 44

This patient has a spontaneous retroperitoneal hematoma compressing the lumbar nerve plexus.

Question 45

 

A 45-year-old man has had gradual onset of progressive weakness to his face and trouble swallowing for 2 days. On examination, he has bilateral ptosis with dilated, poorly reactive pupils, bilateral upper and lower facial muscle weakness, poor soft palate rise, and slurred speech. His oral mucosa is dry. Arms and legs have 5/5 strength. He has no sensory deficits. He has a palpable distended bladder. His symptoms have not abated since onset, and they are getting worse. What is the most likely diagnosis?

• a. 
  Brainstem stroke
• b. 
  Botulism
• c. 
  Muscular dystrophy
• d. 
  Myasthenia gravis
• e. 
  Organophosphate poisoning

Answer 45

This patient has acute onset of progressive neuromuscular junction weakness. He has autonomic findings of abnormal pupil response to light, dry oral mucosa from decreased salivary production, and a distended bladder. These imply that his problem is with the release of acetylcholine (ACh) rather than the nicotinic receptor. The latter would not have autonomic findings. The most appropriate cause of acute onset, progressive impairment in the release of ACh, as listed in the choices, is botulism.