Weakness
Andy S. Jagoda
Melissa Villars
CLINICAL CHALLENGE
Neurologic weakness is a decrease in muscle strength or power; weakness is also a general term commonly used by patients to describe a state of low energy. Neurologic weakness may be a focal symptom, involving a single muscle group, or it may be generalized. A chief complaint of weakness requires a systematic history and physical to develop a working differential diagnosis and to direct testing. Clarification of what the patient means by “weakness” and a distinction between low energy versus diffuse motor weakness versus focal motor weakness is the starting point of the evaluation. The emergency department (ED) approach takes into account the possible, and at times rare, life-threatening causes including stroke, spinal cord lesions, toxic exposures, metabolic abnormalities, botulism, myasthenia gravis, and Guillain-Barré syndrome (GBS), among others. In evaluating weakness, the clinician must always consider disorders that can precipitously compromise the respiratory and functional status of the patient; see Chapter 7: Myopathies and Neuromuscular Junction Disorders for a more detailed evaluation of respiratory decompensation.
DIFFERENTIAL DIAGNOSIS
The differential diagnosis of the weak patient is divided into two broad categories: non-neurologic and neurologic causes, although there is overlap between the categories. Generally speaking, neurologic causes present with decreased neuromuscular power or focal abnormality on examination, whereas non-neurologic causes present as a feeling of global fatigue or asthenia and have a much broader list of possible differential diagnoses (Figure 4.1). The patient’s age is an important consideration in developing the differential diagnosis of weakness. Elderly patients have a higher incidence of comorbid medical conditions than their younger counterparts and are at higher risk of acute central nervous system (CNS) and cardiovascular events. They are more likely to present with occult infections and metabolic disorders that are symptomatically manifested as weakness. In the pediatric age group, sepsis, dehydration, and electrolyte abnormalities are the leading causes of weakness. Infantile botulism and intussusception are two rare but important considerations. Infantile botulism may be seen in children days old to more than 1 year of age. This variant of botulism is much more common than food borne or wound botulism; it presents with weakness, poor tone, poor suck, and/or constipation.
 Figure 4.1: Weakness differential diagnoses. ALS, amyotrophic lateral sclerosis; CVA; GBS, Guillain-Barré syndrome; ICH, intracerebral hemorrhage; MS, multiple sclerosis. |
Neurologic
Cerebral Lesions
Structural lesions in the CNS, such as tumors, strokes, and multiple sclerosis plaques, generally present with focal weakness though some lesions especially in the posterior circulation may present with nonfocal complaints, for example, difficulty swallowing, talking, or breathing, in addition to weakness. Strokes generally present with focal weakness in an anatomic distribution, see Chapter 15: Stroke. Intercranial hemorrhages may present with generalized weakness or have a focal finding on examination depending on the location and size of the hemorrhage.
Spinal Cord Lesions
Lesions in the spinal canal such as epidural hematoma and other vascular diseases, abscess, and metastatic disease can result in weakness that is either symmetric or asymmetric and distal to the site of compromise. Transverse myelitis is an infrequent yet debilitating demyelinating disease of the spinal cord presenting with an acute onset of back pain, lower extremity weakness or paralysis, and sensory deficit. This disease should be suspected in a patient with a recent viral illness presenting with both weakness and sensory deficit below a cord level; it should not be confused with GBS, which will typically demonstrate sparing of the anal sphincter and hyporeflexia with progressive weakness in an ascending pattern over days to a week. Clinical findings of transverse myelitis generally progress over 24 hours and include diminished or absence of strength and sensation below the level of involvement, sphincter dysfunction, hyperreflexia, and urinary incontinence or retention. Spinal epidural abscess also deserves special mention; early presentations can be nonspecific and thus the diagnosis initially missed may potentially lead to disastrous outcomes, see Chapter XXX: CNS Infections.
Neuromuscular Diseases
This group of diseases presents with weakness, the origin of which can be at the neuromuscular junction (eg, myasthenia gravis), the peripheral nerve (eg, GBS), or the muscle (eg, metabolic derangements, medications, and inflammatory states).
Non-neurologic
Infections
All infections can potentially cause weakness, either through general dehydration or through nonspecific mechanisms, such as those seen with mononucleosis or hepatitis. Specific toxins can also cause neurologic weakness, for example, poliomyelitis, botulism, or tick paralysis. The human immunodeficiency virus (HIV) can directly or indirectly cause the full spectrum of weaknesses, from nonspecific fatigue to neuropathies and myelopathies.
Metabolic
Metabolic derangements that can present with weakness include hypoxia, hyperthermia, and alterations in serum glucose and electrolytes. Frequently encountered metabolic causes of weakness include hypoglycemia, hypo- and hyperkalemia. Severe hypokalemia presents with generalized weakness and even paralysis. It can be medication induced as in the case of diuretic use, gastrointestinal loss, or rarely in association with genetic disorders such as familial periodic paralysis. Hyperkalemia not only can affect myocardial function but also may cause an ascending paralysis, ultimately leading to respiratory failure. During the summer, elderly patients with heat exhaustion will frequently present to the ED with generalized weakness because of dehydration and inability to regulate their temperature. A buildup of waste products like CO2 in individuals with chronic obstructive pulmonary disease (COPD), urea in patients with renal failure, and bilirubin in liver failure can also lead to generalized weakness.
Cardiovascular
Acute myocardial infarction (AMI) may present with weakness as the only complaint, especially in the elderly. As the population ages, more patients will present with atypical complaints of myocardial infarction such as weakness or shortness of breath. Myocarditis is another serious but often missed cause of weakness in a patient with a recent viral infection, and these patients may present with a primary complaint of weakness without chest pain. Other cardiovascular causes of weakness
associated with light-headedness or presyncope are due to transient decreased cerebral perfusion, for example, postural hypotension, cervical artery insufficiency, aortic stenosis, cardiac dysrhythmias, and states of decreased cardiac output.
associated with light-headedness or presyncope are due to transient decreased cerebral perfusion, for example, postural hypotension, cervical artery insufficiency, aortic stenosis, cardiac dysrhythmias, and states of decreased cardiac output.
Medications and Toxins
Prescription medications are a common cause of generalized weakness especially in the elderly (Table 4.1). Beta-blockers are particularly noteworthy. There are usually no focal findings on examination and individual muscle strength testing is normal. In one study of 106 patients with a chief complaint of weakness and dizziness, 9% of all patients and 20% of those older than age 60 had symptoms attributed to prescription medications.1,2
Certain toxins can present with the sudden onset of neurologic weakness: Organophosphates and carbamates act at the neuromuscular junction by inhibiting acetylcholinesterase. Patients present with a constellation of symptoms including lacrimation, defecation, salivation, and weakness, which can progress rapidly to paralysis and respiratory failure. In contrast, poisonings from heavy metals can be subtle and present with a slowly progressive course. Carbon monoxide may present with generalized weakness and headache as their only complaint. This diagnosis should be considered in patients presenting with weakness especially during the winter months when space heaters are often used.
Endocrine
Hypothyroidism is the most common endocrine cause of weakness and is frequently not diagnosed early in its presentation. Thyrotoxic periodic paralysis with alternations in potassium regulation can present with weakness as a primary complaint. Adrenal insufficiency, often induced by chronic
steroid use, may present with weakness because of hypotension, hyperkalemia, and/or hyponatremia. The diabetic patient with hyperglycemia can present with generalized weakness from ketoacidosis, dehydration, or altered potassium. Cobalamin deficiency (vitamin B12), which is most commonly seen with pernicious anemia, may present with lower extremity weakness, paresthesias, and tongue discomfort and has a macrocytic anemia on laboratory analysis.
steroid use, may present with weakness because of hypotension, hyperkalemia, and/or hyponatremia. The diabetic patient with hyperglycemia can present with generalized weakness from ketoacidosis, dehydration, or altered potassium. Cobalamin deficiency (vitamin B12), which is most commonly seen with pernicious anemia, may present with lower extremity weakness, paresthesias, and tongue discomfort and has a macrocytic anemia on laboratory analysis.
TABLE 4.1 Commonly Used Drugs and Other Substances Associated with Weakness | ||||||||||||||||||||||
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Rheumatologic
Weakness is a prominent complaint of most rheumatologic diseases and occasionally is the primary presenting symptom. Diseases to consider include systemic lupus erythematosus, polymyositis, dermatomyositis, and polymyalgia rheumatica.
Psychogenic Weakness
A psychiatric diagnosis as a cause of weakness is one of exclusion and almost never made in the acute setting. Patients with conversion disorder may present with paralysis of a specific muscle group that is not anatomically consistent. The symptoms of these patients are subconscious, which is in contrast to the malingering patient, whose actions are purposeful and often have secondary gain. Patients with depression may also experience generalized weakness secondary to the profound fatigue common to the illness.
APPROACH
A key first step is differentiating loss of neuromuscular power from the sensation of generalized weakness. This may be complicated by the fact that presentations are not strictly binary; for example, hypothyroidism may present with general fatigue plus a myopathy. The history begins with elucidating the location of the complaint and whether it is symmetrical, focal, or generalized; other features include the acuity of onset and duration of symptoms, exacerbating and mitigating factors, and presence of associated symptoms.
Because neuromuscular weakness is the inability to perform a desired movement with normal force and power due to a reduction in muscle strength and function, these patients are likely to complain of an inability to perform specific tasks. Asking open-ended questions such as “what activities can you no longer do?” may be a good place to start with a patient having difficulty explaining their weakness in detail. Also, asking task-specific questions such as “are you having any difficulty brushing teeth, combing hair, rising from a chair, walking upstairs, opening a jar or door, etc.” can be helpful primers to jump-start the dialogue for the patient. Patients who are unable to respond to questions about specific tasks and give more generalized histories of weakness are more likely to have a non-neuromuscular etiology.
Sudden onset of weakness suggests a vascular catastrophe, such as a spinal cord hemorrhage, and requires emergent evaluation. A slower progression of symptoms may suggest a metabolic disorder such as hyperkalemia, or disorders such as GBS or myasthenia gravis. A history of symmetric ascending weakness in a patient with a recent respiratory illness will aid in the diagnosis of GBS. The weakness of myasthenia gravis may fluctuate, and a careful history is needed to elicit a progression of symptoms throughout the day or an association with exercise, temperature extremes, such as hot showers, or repeated activity, such as chewing or combing one’s hair.
Recent illness, other medical problems, occupational history, travel history, history of tick bites, use of medications, and use of recreational drugs are all important factors to assess in the patient complaining of weakness. A thorough review of systems includes inquiry about recent weight loss, fever or sweats, visual changes (including diplopia), difficulty swallowing, joint or muscle pain, palpitations, change in bowel habits, and skin rashes. Occupational or recreational exposures may indicate drug toxicity.
The physical examination begins with a full set of vital signs including oxygen saturation and a finger blood glucose. A blood glucose level should be obtained early during the evaluation, as hypoglycemia may present with an array of symptoms, including weakness. Capnometry may be useful in identifying and monitoring patients with weakness associated with compromised ventilation and is supplemented with obtaining a forced vital capacity or negative inspiratory force measurements. Tachycardia, with or without hypotension, suggests volume depletion including anemia, or toxic drug ingestion. Rectal temperature measurement is particularly important in that
infections frequently present with nonspecific complaints, such as weakness. The ears, sinuses, thyroid, and cardiac status should be assessed, as well as a careful evaluation for signs of trauma, which may suggest physical abuse.
infections frequently present with nonspecific complaints, such as weakness. The ears, sinuses, thyroid, and cardiac status should be assessed, as well as a careful evaluation for signs of trauma, which may suggest physical abuse.
TABLE 4.2 Motor Strength Grading System (Medical Research Council Scale) | ||||||||||||||
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