Weakness

Many patients report weakness when their problem is fatigue Fatigue Fatigue is difficulty initiating and sustaining activity due to a lack of energy and accompanied by a desire to rest. Fatigue is normal after physical exertion, prolonged stress, and sleep deprivation... read more . Fatigue can prevent maximal effort and muscle performance during strength testing.

Common causes of fatigue include acute severe illness of almost any cause, cancers, chronic infections (eg, HIV infection Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection results from 1 of 2 similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain... read more , hepatitis Causes of Hepatitis Hepatitis is inflammation of the liver characterized by diffuse or patchy necrosis. Hepatitis may be acute or chronic (usually defined as lasting > 6 months). Most cases of acute viral hepatitis... read more , endocarditis Infective Endocarditis Infective endocarditis is infection of the endocardium, usually with bacteria (commonly, streptococci or staphylococci) or fungi. It may cause fever, heart murmurs, petechiae, anemia, embolic... read more , mononucleosis Infectious Mononucleosis Infectious mononucleosis is caused by Epstein-Barr virus (EBV, human herpesvirus type 4) and is characterized by fatigue, fever, pharyngitis, and lymphadenopathy. Fatigue may persist weeks or... read more ), endocrine disorders, renal failure Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more , hepatic failure Acute Liver Failure Acute liver failure is caused most often by drugs and hepatitis viruses. Cardinal manifestations are jaundice, coagulopathy, and encephalopathy. Diagnosis is clinical. Treatment is mainly supportive... read more , heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal... read more , and anemia Etiology of Anemia Anemia is a decrease in the number of red blood cells (RBCs), which leads to a decrease in hematocrit and hemoglobin content. (See also Red Blood Cell Production.) The RBC mass represents the... read more . Multiple sclerosis can cause daily fatigue that increases with exposure to heat and humidity.

Patients with fibromyalgia Fibromyalgia Fibromyalgia is a common, incompletely understood nonarticular, noninflammatory disorder characterized by generalized aching (sometimes severe); widespread tenderness of muscles, areas around... read more , depression Depressive Disorders Depressive disorders are characterized by sadness severe enough or persistent enough to interfere with function and often by decreased interest or pleasure in activities. Exact cause is unknown... read more , or chronic fatigue syndrome Chronic Fatigue Syndrome Chronic fatigue syndrome (CFS, also called myalgic encephalomyelitis/chronic fatigue syndrome [ME/CFS]) is a syndrome of life-altering fatigue lasting > 6 months that is unexplained and is accompanied... read more may report weakness or fatigue but have no defined objective abnormalities.

History of present illness should begin with open-ended questions, asking patients to describe in detail what they are experiencing as weakness. Then, specific questions can be asked, particularly about the ability to do specific tasks, including brushing teeth or hair, speaking, swallowing, rising from a chair, climbing stairs, and walking.

Clinicians should also ask about the onset of weakness (sudden or gradual) and progression (eg, constant, worsening, intermittent) of symptoms. Close questioning is needed to differentiate sudden onset from sudden recognition; patients may suddenly recognize symptoms only after slowly progressive weakness crosses a threshold that prevents them from doing some normally routine task (eg, walking, tying shoes).

Important associated symptoms include sensory changes, double vision, memory loss, difficulty using language, seizures, and headaches. Factors that worsen weakness, such as heat (suggesting multiple sclerosis) or repetitive use of a muscle (suggesting myasthenia gravis), are noted.

Review of systems should seek symptoms suggesting possible causes, including the following:

Past medical history should identify known disorders that can cause weakness or fatigue, including

Clinicians should assess risk factors for possible causes, including those for infection (eg, unprotected sexual intercourse, blood transfusions, exposure to tuberculosis) and stroke (eg, hypertension, atrial fibrillation, atherosclerosis).

Complete drug history should be reviewed.

Family history should include known hereditary disorders (eg, hereditary muscle disorders, channelopathies, metabolic myopathies, hereditary neuropathies) and presence of similar symptoms in family members (suggesting a possible unrecognized hereditary disorder). Hereditary motor neuropathies often go unrecognized in families because of variable, incomplete phenotypic expression. Hammer toes, high arches in the feet, and poor performance in sports may indicate an undiagnosed hereditary motor neuropathy.

Social history should note the following:

A complete neurologic and muscle examination is done to identify localizing or diagnostic findings. Key findings usually involve

Cranial nerve examination How to Assess the Cranial Nerves (See also Neuro-ophthalmologic and Cranial Nerve Disorders and Introduction to the Neurologic Examination.) Smell, a function of the 1st (olfactory) cranial nerve, is usually evaluated only... read more includes inspection of the face for gross asymmetry and ptosis; mild facial asymmetry can be normal. Extraocular movements and facial muscles, including masseters (for strength), are tested. Palatal weakness is suggested by a nasal voice quality; testing the gag reflex and looking at the palate directly are less helpful. Tongue weakness is suggested by inability to clearly articulate certain consonants (eg, saying "ta-ta-ta") and slurring of speech (lingual dysarthria). Mild asymmetry during tongue protrusion may be normal. Sternocleidomastoid and trapezius strength is tested by having the patient rotate the head and shrug the shoulders against resistance. The patient is asked to blink repeatedly to see whether blinking fatigues.

Motor examination How to Assess the Motor System The limbs and shoulder girdle should be fully exposed, then inspected for the following: Atrophy Hypertrophy Asymmetric development Fasciculations read more includes inspection, assessment of tone, and strength testing. The body is inspected for kyphoscoliosis (sometimes suggesting chronic weakness of paraspinal muscles) and for surgical and traumatic scars. Dystonic posturing (eg, torticollis) may interfere with movement, mimicking weakness. Muscles are inspected for fasciculations and atrophy; both may begin focally or asymmetrically in ALS. Fasciculations may be most visible in the tongue in patients with advanced ALS. Diffuse atrophy may be most evident in the hands, face, and shoulder girdle.

Muscle tone is assessed using passive motion. Tapping a muscle (eg, hypothenar) may induce fasciculations in neuropathies or a myotonic contraction in myotonic dystrophy.

Strength testing How to Assess Muscle Strength Patients who report weakness may mean fatigue, clumsiness, or true muscle weakness. Thus, the examiner must define the precise character of symptoms, including exact location, time of occurrence... read more should include muscles that are proximal, distal, extensor, and flexor. Some tests of large, proximal muscles include standing from a sitting position; squatting and rising; and flexing, extending, and turning the head against resistance.

Motor strength is often rated on a 0 to 5 scale:

Although these numbers seem objective, rating strength between 3 and 5 (the typical levels during early weakness, when diagnosis usually occurs) is rather subjective; if symptoms are unilateral, comparison with the unaffected side improves discrimination. Describing specifically what the patient can or cannot do is often more useful than simply assigning a number for level of weakness, particularly for assessing changes in weakness over time. A cognitive deficit may cause motor impersistence (inability to focus attention on completing a motor task), motor perseveration, apraxia, or incomplete effort. Malingering and other functional weakness is often characterized by give-way weakness, in which normal strength of effort suddenly gives way.

Coordination testing How to Assess Gait, Stance, and Coordination Normal gait, stance, and coordination require integrity of the motor, vestibular, cerebellar, and proprioceptive pathways ( see also Movement and Cerebellar Disorders). A lesion in any of the... read more includes finger-to-nose and heel-to-shin maneuvers and toe-heel tandem gait to check for cerebellar dysfunction, which can accompany cerebellar stroke, vermian atrophy (eg, due to alcohol abuse), some hereditary spinocerebellar ataxias Hereditary ataxias Cerebellar disorders have numerous causes, including congenital malformations, hereditary ataxias, and acquired conditions. Symptoms vary with the cause but typically include ataxia (impaired... read more , multiple sclerosis Multiple Sclerosis (MS) Multiple sclerosis (MS) is characterized by disseminated patches of demyelination in the brain and spinal cord. Common symptoms include visual and oculomotor abnormalities, paresthesias, weakness... read more , and the Miller Fisher variant of Guillain-Barré syndrome Guillain-Barré Syndrome (GBS) Guillain-Barré syndrome is an acute, usually rapidly progressive but self-limited inflammatory polyneuropathy characterized by muscular weakness and mild distal sensory loss. Cause is thought... read more .

Gait is observed for the following:

Walking on the toes and heels is tested; distal muscle weakness makes these maneuvers difficult. Walking on the heels is particularly difficult when corticospinal tract lesions are the cause of weakness. Spastic gait is notable for scissoring (legs flexed slightly at the hips and knees, giving the appearance of crouching, with the knees and thighs hitting or crossing in a scissors-like movement) and walking on the toes. A steppage gait and foot drop may occur with peroneal nerve palsy.

Sensation How to Assess Sensation For the ability to sense a sharp object, the best screening test uses a safety pin or other sharp object to lightly prick the face, torso, and 4 limbs; the patient is asked whether the pinprick... read more is tested; sensory deficits can help localize some lesions causing weakness (eg, sensory level localizes the lesion to a spinal cord segment) or suggest certain specific causes of weakness (eg, distal sensory loss helps confirm clinical suspicion of Guillain-Barré syndrome).

A truncal bandlike tingling and pressure in a dermatomal distribution is a spinal cord sign that occurs with both intrinsic and extrinsic lesions.

Reflexes How to Assess Reflexes (See also Introduction to the Neurologic Examination) Deep tendon (muscle stretch) reflex testing evaluates afferent nerves, synaptic connections within the spinal cord, motor nerves, and descending... read more are tested. If deep tendon reflexes appear absent, they may be elicited by augmentation with Jendrassik maneuver (eg, trying to pull the hands apart while they are clasped together). Hyporeflexia may be normal throughout life or occur with aging, but findings should be symmetric and augmentation should elicit reflexes that are otherwise absent. The plantar reflex (extensor, flexor) is tested. The following responses suggest certain disorders or locations of lesions:

Evaluation also includes

If patients have no objective motor weakness, the general examination is particularly important; in such patients, nonneuromuscular disorders should be sought.

Signs of respiratory distress (eg, tachypnea, weak inspiration) are noted. The skin is examined for jaundice, pallor, rash, and striae. Other important findings during inspection include the moon facies of Cushing syndrome and the parotid enlargement, smooth hairless skin, ascites, and vascular spiders of chronic alcohol use.

The neck, axillae, and inguinal area should be palpated for adenopathy; any thyromegaly is noted.

Heart and lungs are auscultated for crackles, wheezes, prolonged expiration, murmurs, and gallops.

The abdomen is palpated for masses, including, if spinal cord dysfunction is possible, a grossly enlarged bladder.

A rectal examination is done to check for heme-positive stool.

Joint range of motion is assessed.

If tick paralysis is suspected, the skin, particularly the scalp, should be thoroughly inspected for ticks.

The following findings are of particular concern:

The history helps differentiate weakness from fatigue, defines the time course of the illness, and gives clues to the anatomic pattern of weakness. Weakness and fatigue tend to cause different symptoms:

The temporal pattern of symptoms is useful.

The anatomic pattern of weakness is characterized by specific motor tasks that are difficult to do. Anatomic patterns suggest certain diagnoses:

Physical examination further helps localize the lesion. First, general patterns are discerned:

Additional findings can help localize the lesion more precisely. For example,

Weakness with lower motor neuron signs may result from a disorder affecting one or more peripheral nerves; such a disorder has very specific patterns of weakness (eg, wristdrop in radial nerve injury). When the brachial or lumbosacral plexus is damaged, motor, sensory, and reflex deficits are often patchy and do not follow any one peripheral nerve pattern.

Sometimes combinations of findings suggest a cause (see table Findings Related to Weakness Suggesting a Specific Disorder Findings Related to Weakness Suggesting a Specific Disorder ).

If no symptoms or signs of true weakness (eg, characteristic anatomic and temporal pattern, objective signs) are present and patients complain only of overall weakness, fatigue, or lack of energy, clinicians should consider nonneurologic disorders. However, among older patients who feel too weak to walk, determining the contribution of muscle weakness may be difficult because gait dysfunction is often multifactorial (see page Geriatrics Essentials Geriatrics Essentials: Weakness Weakness is one of the most common reasons patients present to primary care clinicians. Weakness is loss of muscle strength, although many patients also use the term when they feel generally... read more ).

Patients with many disorders may be functionally limited but lack true loss of muscle strength. For example, cardiopulmonary dysfunction or anemia can cause fatigue due to dyspnea or exercise intolerance. Joint dysfunction (eg, due to arthritis) or muscle pain (eg, due to polymyalgia rheumatica or fibromyalgia) may make doing physical tasks difficult. These and other physical disorders that cause complaints of weakness (eg, influenza, infectious mononucleosis, renal failure) typically are already diagnosed or are suggested by findings during the history, physical examination, or both.

In general, if history and physical examination do not detect abnormalities suggesting physical disorders, these disorders are unlikely; disorders that cause constant, generalized fatigue with no physiologic temporal or anatomic pattern (eg, depression; chronic fatigue syndrome; an as-yet undiscovered systemic illness such as severe anemia, hypothyroidism, or Addison disease; an adverse drug effect) should be considered.

In patients with fatigue Evaluation Fatigue is difficulty initiating and sustaining activity due to a lack of energy and accompanied by a desire to rest. Fatigue is normal after physical exertion, prolonged stress, and sleep deprivation... read more rather than weakness, history and physical examination focus on identifying subtle manifestations of underlying illness (particularly infections, endocrine and rheumatologic disorders, anemia, and depression) that can be used to guide testing, but testing may be unnecessary.

Although many tests can be done if patients have true muscular weakness, such testing is often only adjunctive.

If no true weakness is present, other clinical findings (eg, dyspnea, pallor, jaundice, heart murmur), if present, are used to guide testing.

If patients have no abnormal clinical findings, test results are unlikely to be abnormal. In such cases, testing practices vary widely. Initial tests usually include some combination of a complete blood count (CBC), electrolytes (including calcium and magnesium), glucose, kidney and liver function tests, thyroid-stimulating hormone (TSH), erythrocyte sedimentation rate (ESR), and hepatitis C serologic testing.

If sudden or severe true general weakness or any respiratory symptoms are present, forced vital capacity and maximal inspiratory force must be tested to assess risk of acute ventilatory failure. Patients with vital capacity < 15 mL/kg or inspiratory force < 20 cm H2O are at increased risk.

If true weakness is present (and usually after risk of acute ventilatory failure is assessed), initial testing typically focuses on determining the mechanism of weakness. Unless the cause is obvious, routine laboratory tests (CBC, electrolytes [including calcium and magnesium], glucose, kidney and liver function tests, TSH, ESR, hepatitis C serologic testing) are usually done.

Tests done to determine the location and mechanism of weakness depend on clinical findings.

If brain upper motor neuron dysfunction is suspected, the key test is MRI. CT is used when MRI testing is not possible (eg, in patients with a cardiac pacemaker).

If myelopathy is suspected, MRI can detect lesions in the spinal cord. It also detects other causes of paralysis that may mimic myelopathy, including lesions of the cauda equina, spinal roots, and brachial and lumbosacral plexuses. CT myelography may be used when MRI testing is not available. Other tests are done (see table Some Causes of Muscle Weakness Some Causes of Muscle Weakness ). Cerebrospinal fluid (CSF) analysis may be unnecessary for some disorders diagnosed during imaging (eg, epidural tumor) and is contraindicated if CSF block (eg, due to epidural spinal cord compression) is suspected.

If polyneuropathies, myopathies, or neuromuscular junction disorders are suspected, the key tests that help differentiate these mechanisms of weakness are electrodiagnostic studies (electromyography and nerve conduction studies).

After nerve injury, changes in nerve conduction and muscle denervation can take up to a few weeks to develop, so electrodiagnostic studies may not help when the disorder is acute. However, these studies can help differentiate among certain acute disorders, such as acute demyelinating neuropathy (eg, Guillain-Barré syndrome), acute botulism, and other acute neuromuscular junction disorders.

If myopathy is suspected (suggested by muscle weakness, muscle cramping, and pain), muscle enzymes (eg, creatine kinase [CK], aldolase, lactic dehydrogenase [LDH]) may be measured. Elevated levels are consistent with myopathy but can also be high in neuropathies (reflecting muscle atrophy) and very high in ischemic rhabdomyolysis. Also, levels may not be high in all myopathies. Regular crack cocaine use can also cause chronically moderately elevated CK levels (mean value, 400 IU/L).

Clinicians can use MRI to identify muscle inflammation, as occurs in inflammatory myopathies. Muscle biopsy may be necessary ultimately to diagnose myopathy or myositis. MRI or electromyography can help find a suitable site for muscle biopsy. However, needlestick artifact can mimic muscle pathology and must be avoided; thus, biopsy should never be done in the same muscle tested by electromyography.

Genetic testing can help confirm certain hereditary myopathies.

If motor neuron disorders Amyotrophic Lateral Sclerosis (ALS) and Other Motor Neuron Diseases (MNDs) Amyotrophic lateral sclerosis and other motor neuron diseases are characterized by steady, relentless, progressive degeneration of corticospinal tracts, anterior horn cells, bulbar motor nuclei... read more (eg, ALS) are suspected, tests include electromyography and nerve conduction studies to confirm the diagnosis and exclude treatable disorders that mimic motor neuron disorders (eg, chronic inflammatory demyelinating polyneuropathy, multifocal motor neuropathy with conduction block). Brain MRI may show degeneration of the corticospinal tracts when ALS is advanced. Spinal cord MRI (or CT myelography) is done routinely to rule out spinal cord compression or other myelopathies (see table Some Causes of Muscle Weakness Some Causes of Muscle Weakness ).

Testing for specific disorders may be needed: