Chapter 48
Weakness Developing in the Intensive Care Unit Patient
There are numerous causes of generalized weakness that may develop in patients in the intensive care unit (ICU). Weakness may result from dysfunction of the central nervous system (CNS), the peripheral nervous system, or both. Causes of weakness that developed de novo in the setting of critical illness are discussed here. Disorders that develop in the ICU setting are generally separated from disorders that produce weakness severe enough to result in ICU admission, such as myasthenia gravis or the Guillain-Barré syndrome (see Chapter 67). Patients with a preexisting neuromuscular disorder, such as amyotrophic lateral sclerosis, may also present for ICU admission with acute weakness in the setting of another illness (such as infection).
The differential diagnosis of acute, generalized weakness is aided by clues from the history and neurologic examination, as summarized in Tables 48.1 and 48.2. If it is unknown whether the weakness predated the current ICU period, then the differential diagnosis should also include the entities that may produce weakness that necessitates ICU care (see Table 67.2).
TABLE 48.1
Acute, Unilateral Weakness Developing in the ICU Patient
| Cause by Localization | Suggestive Clinical Features | Diagnostic Tests |
| Stroke—ischemic or hemorrhagic | Face and arm often weaker than leg Risk factors, such as atrial fibrillation, MI, endocarditis or bleeding diathesis/anticoagulation (ICH) | MRI (brain)∗ |
| Seizure—after a pronged seizure (Todd’s paralysis) or with nonconvulsive status epilepticus | History of prior seizure(s) or witnessed seizure Underlying structural lesion common | EEG† and MRI (brain) |
| Spinal cord—lateral compression by epidural abscess, tumor, or hemorrhage | Back or neck pain No involvement of face Sensory level (see Figure 102-1) Arms may be spared in thoracic or lumbar lesions | MRI (cervical, thoracic, or lumbar spine) |
∗Other studies commonly include CTA or MRA of head and neck, echocardiogram, telemetry, and carotid ultrasound.
TABLE 48.2
Acute, Generalized Weakness Developing in the ICU Patient∗
| Cause by Localization | Suggestive Clinical Features | Diagnostic Tests |
| Brain† | Unresponsiveness with quadriparesis | |
| Encephalopathy (sepsis, sedating drug, renal or hepatic failure) | Severe infection Known renal or hepatic disease | Blood cultures; imaging for infections Renal and hepatic blood studies |
| Bilateral structural lesion (strokes, SAH, herniation secondary to increased intracranial pressure) | Onset with unilateral weakness Asymmetrically enlarged pupil | CT scan (brain), MRI (brain) |
| Nonconvulsive status epilepticus | History of seizures; rapid fluctuation of responsiveness | Prolonged EEG monitoring |
| Brain Stem | Ocular motor abnormalities common | |
| Brain stem stroke | May be unresponsive or awake | MRI (brain) |
| Central pontine myelinolysis | Rapid correction of severe hyponatremia | MRI (brain) |
| Spinal Cord | Sensory level; early urinary retention; spares cranial muscles | |
| Acute epidural compression (abscess, hemorrhage, tumor) | History of infection, tumor or bleeding Back or neck pain Weakness may be limited to the legs (in thoracic cord lesions) | MRI (cervical, thoracic, or lumbar spine) |
| Other causes (cord hemorrhage) | Risk for hemorrhage | MRI (cervical or thoracic spine) |
| Peripheral Nerve | Weakness, with sensory and reflex loss | |
| Critical illness polyneuropathy‡ | Develops after period of crucial illness | EMG; NCS |
| Neuromuscular Junction | Weakness, without sensory or reflex loss | |
| Prolonged pharmacologic neuromuscular blockade | History of neuromuscular blocking agents and renal or hepatic dysfunction | Train-of-five; or EMG with RNS studies |
| Hypermagnesemia | History of renal failure | Serum magnesium |
| Muscle | Weakness, without sensory or reflex loss | |
| Critical illness myopathy‡ | Develops after period of crucial illness; often history of corticosteroid or NMBA use | EMG |
| Severe hypokalemia | History of hypokalemia, diuretic use, or renal tubular acidosis | Serum potassium |
∗This is for de novo weakness in the ICU setting; for a full differential diagnosis of weakness add Table 67.2.
†The level of obtundation should be significant enough to produce quadriparesis with these disorders (see text).
‡Critical illness (i.e., severe sepsis) is the presumptive cause of these disorders.
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