Weakness (Case 58)

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Chapter 66
Weakness (Case 58)

Edward H. Yu MD and Maya Katz MD

Case: The patient is a 66-year-old retired man presenting with right upper extremity weakness for several days. His daughter brought him to the hospital after finding that he was unable to hold objects in his right hand during her weekly visit with him. His past medical history includes diabetes mellitus and hypertension. A comprehensive history and neurologic exam performed in the ED revealed that the patient awoke with his symptoms 3 days before his daughter’s visit and that his weakness has been constant, with no change in its severity. On exam, he can barely move his right upper extremity against gravity. In addition, he has increased tone and is hyperreflexic in the same extremity. A right-sided Babinski reflex is also present.

Differential Diagnosis

Central nervous system

Peripheral nervous system




Guillain-Barré syndrome (GBS)

Multiple sclerosis (MS)

Myasthenia gravis

Spinal cord injury



Speaking Intelligently

When a patient presents with weakness, you should immediately assess whether the patient has a peripheral (lower motor neuron) or a central (upper motor neuron) nervous system abnormality. While taking the history and performing the neurologic exam, consider whether the dysfunction is in the brain, spinal cord, spinal nerve roots, peripheral nerves, neuromuscular junction, or muscles. A comprehensive history followed by a good neurologic examination should provide the foundation for determining where the abnormality lies. Imaging, laboratory, and electrophysiologic studies are useful diagnostic adjuncts and confirm the anatomic location and etiology of the abnormality. Since treatments for weakness vary widely based on the etiology of the symptoms, accurate diagnosis is critical to providing effective care. Patients with diseases that cause weakness are often significantly disabled. An interdisciplinary team that includes rehabilitation specialists, neurosurgeons, pain specialists, and mental health professionals can be invaluable to the patient’s recovery.



Clinical Thinking

• Due to the huge scope of possible etiologies, the history and physical exam is essential in pinning down the most likely causes of weakness in a patient.

• Direct particular attention toward the progression and pattern of weakness, the onset and timing of weakness, and any associated symptoms, such as sensory abnormalities and speech difficulties.

• Categorizing the physical exam findings in a systematic manner allows for an anatomic localization of the disease process. A differential diagnosis can then be generated once the anatomic basis has been established.

• Correlating the presentation with the anatomic localization allows the clinician to formulate a working diagnosis.


• When a patient reports weakness, it can mean a variety of different things. For example, the patient may be feeling general malaise, or he or she may be referring to weakness of specific muscle groups. It is important to identify the location of the weakness, time of onset, duration and severity of the symptoms, and whether the weakness changes over the course of the day.

• Obtaining a history of any associated symptoms, such as any pain or sensory symptoms, is extremely important in narrowing down the differential diagnosis (numbness suggests neuropathy while pain suggests radiculopathy).

• The past medical history can identify risk factors for specific diseases (e.g., hypertension and diabetes are risk factors for stroke).

• Certain rare causes of weakness may be congenital (e.g., spinal muscular atrophy); therefore, a family history should be obtained.

Physical Examination

• The physical exam should focus on (1) gross observation for any abnormal or involuntary movements; (2) inspection of muscle bulk and tone; (3) palpation and percussion for tenderness and involuntary contractions; (4) muscle strength testing; (5) reflex testing (deep tendon reflexes and extensor plantar [Babinski] reflex); (6) sensory testing (particularly the pattern of deficits and any correlation with the site of weakness); and (7) cranial nerve involvement.

• Inspection of muscle bulk and tone can give clues as to whether the focus is lower motor neuron (atrophy and fasciculations) or upper motor neuron (increased tone, spasticity). Severe atrophy can also give clues to the time course and chronicity of weakness. Strength testing should be done systematically, comparing each major muscle group to the contralateral side. Subtle weakness can be detected with side-to-side comparison of limbs held against gravity (e.g., pronator drift). If indicated, checking the patient for muscle fatigue with simple repetitive exercise (e.g., maintaining abduction of the shoulder against resistance for 1 minute) can help identify neuromuscular junction disease (e.g., myasthenia gravis).

• Reflex testing is essential in differentiating lower motor neuron from upper motor neuron causes of weakness. Patients with upper motor neuron problems usually have hyperreflexia, whereas patients with lower motor neuron causes often have hyporeflexia. As with strength testing, comparison with the contralateral side is often helpful. Additional upper motor neuron findings include a positive Babinski reflex. Lower motor neuron findings are usually confined to atrophy of the weak limb or muscle, with hyporeflexia and possible fasciculations.

Tests for Consideration

Serum creatine kinase (CK): CK elevation is classically seen in muscle damage from any cause, particularly inflammatory myopathies and glycogen storage diseases. Other causes of elevated CK include prolonged exercise, alcohol abuse, trauma, and hypothyroidism.


TSH: TSH levels are elevated in patients with hypothyroidism and decreased in patients with hyperthyroidism. Some patients present with symmetrical proximal muscle weakness with associated myalgia (muscle pain), joint stiffness, and muscle enlargement (in weak muscles) consistent with a hypothyroid myopathy. Other patients present with proximal weakness with atrophy of the shoulder and pelvic girdle muscles, with heat intolerance and fatigue consistent with hyperthyroid myopathy.


Electrophysiology studies: These include nerve conduction studies (NCS), needle electromyography (EMG), and repetitive nerve stimulation (RNS). NCS assess the integrity of motor and sensory peripheral nerves by administering electrical pulses across the nerve being studied. Needle EMG involves insertion of a recording needle into muscle for assessment of underlying disease. Muscle activity at rest and with contraction is assessed for any pathologic patterns of abnormality. RNS is a modified NCS in which a nerve is repeatedly stimulated at a fixed frequency. A combination of these studies can help pinpoint the pathophysiologic mechanism of weakness to a peripheral nervous system process.


LP with CSF analysis: Can help narrow the diagnosis.
Relevant CSF studies are listed in the Clinical Entities section.
Patients suspected of increased ICP should be fully evaluated with physical exam (including funduscopic exam to look for papilledema) and/or imaging studies before an LP to avoid the risk of cerebral herniation.


Biopsies are rarely indicated in patients with weakness. Muscle biopsies may be helpful in differentiating different types of muscle disease.
Nerve and skin biopsies, helpful in certain types of neuropathies, should be done on the affected site.

$1190, $1321, $105



Imaging studies of the CNS are usually necessary.

A CT scan is a fast and inexpensive initial study that can help rule out most CNS causes of weakness.


An MRI scan should be performed if there are any abnormal findings on CT scan or if the history and/or physical exam raises suspicion of a CNS disease.



Clinical Entities Medical Knowledge
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Pathologic changes include areas of necrosis in the brain due to infarction that correlate with specific neurologic deficits. Patients will usually have risk factors for atherosclerosis or embolic disease, such as hypertension, diabetes mellitus, hypercholesterolemia, coronary artery disease, peripheral artery disease, and/or atrial fibrillation. Smoking and excess alcohol intake, as well as a sedentary lifestyle and obesity, are also risk factors for strokes.


Typical features include an acute onset of focal neurologic deficits, which are usually unilateral. The location of the weakness correlates to the areas of damage caused by the stroke. Patients may have associated symptoms, including unilateral sensory loss, as well as weakness in facial muscles leading to difficulty with speaking or swallowing.


The specific area of ischemia can be identified using CNS imaging modalities, including CT and MRI.