Neuromuscular Disorders in Medical and Surgical ICUs: Case Studies in Critical Care Neurology
Section snippets
Case 1
A 50-year-old man is admitted to an ICU after colonic surgery. Postoperatively he remains mechanically ventilated after he develops staphylococcus aureus septicemia, hypotension, liver failure, and renal failure requiring continuous venovenous hemofiltration. He is sedated and paralyzed with neuromuscular blockers (NMBs) to control agitation and improve oxygenation. Four weeks later, sedatives and NMBs are discontinued. By this time he has received a cumulative dose of 500 mg of dexamethasone,
Case 2
A 45-year-old man is admitted in a stuporous state to an ICU and immediately is intubated and mechanically ventilated. His sensorium does not improve during 1 week, and he remains ventilator dependent. He develops fever after a day in the ICU. The medical team also notices decreased spontaneous limb movements. All laboratory parameters are normal except for a mild peripheral leukocytosis. Brain CT also is normal. Review of the history reveals that he had been an avid gardener who used to work
Evaluation of patients in ICUs who have generalized weakness
These cases illustrate some of the common problems encountered with patients in ICUs. It often is difficult to ascertain the exact time of onset and pattern of weakness, and weakness is detected incidentally or during attempts to wean patients from the ventilator. The initial step to determine is if a central process or peripheral neuromuscular problem is the cause of weakness. This may be complicated by encephalopathy or sedation (resulting from drugs, metabolic processes, sepsis, seizures, or
Spinal cord disorders
Spinal cord injuries are common in patients who have polytrauma and MRI should be considered in these patients. Ischemic myelopathy should be considered in patients who have a history of aortic surgeries or aortic dissections. Several viruses, including coxsackie, echovirus, herpes, Epstein-Barr, and CMV, are associated with infectious myelitis [7]. Antiviral agents should be considered for specific agents—acyclovir, valacyclovir, or famciclovir for herpes myelitis; acyclovir for Epstein-Barr
Anterior horn cell disorders
Acute poliomyelitis resulting from poliovirus was a leading cause of respiratory failure in the early half of the twentieth century. With its eradication, other viral infections, such as WNV, have taken its place [8]. Severe WNV infection results in a meningoencephalitis and an acute flaccid asymmetric paralysis [9]. The flaccid weakness mimics GBS but is accompanied by fever; encephalopathy; predominantly proximal, asymmetric weakness; electrophysiologic evidence of axonopathy [10]; and CSF
Polyneuropathies
Acquired neuropathy in patients who are critically ill was described first by Brown and colleagues under the rubric, CIP [14]. Recent studies show that CIP and its muscle counterpart, CIM, are among the most common disorders resulting in weakness in patients who are in ICUs [2].
Several conditions, including sepsis, systemic inflammatory response syndrome (SIRS), multiorgan dysfunction syndrome, status asthmaticus, and medications, such as NMB agents, corticosteroids, and cytotoxic drugs, are
Neuromuscular junction disorders
Neuromuscular junction disorders probably are the second most common cause of weakness in ICUs. Common conditions include prolonged neuromuscular blockade, myasthenia gravis, LEMS, and drug-induced or iatrogenic myasthenic syndromes. RNS and assessment of acetylcholine receptor antibody titers are helpful in subtyping the myasthenic syndrome. Iatrogenic or drug-induced myasthenia always should be considered (Box 4). It also must be remembered that all myasthenic patients do not show a uniform
Myopathies
The most common myopathy encountered in patients in ICUs probably is CIM. As it is discussed previously with CIP, further mention is omitted from this section. Among acquired myopathies, inflammatory myopathies are among the most common types encountered in ICUs—DM and polymyositis (PM). DM is easy to recognize by virtue of its accompanying skin rash. The rash is erythematous, periorbital, and purplish and can be accompanied by rashes over the knuckles (Gottron's sign) or subcutaneous
Intracranial disorders
Although neuromuscular causes account for the majority of patients who have generalized weakness, intracranial conditions always should be considered. Posterior circulation strokes (especially pontine infarctions) can result in a locked-in state, where patients are able to communicate only via eye blinks. Multiple strokes can be seen in patients who have underlying infective endocarditis or have undergone cardiac surgery. Depending on the type of cardiac surgery, the frequency of strokes may
Summary
The differential diagnosis of generalized weakness in ICU patients is quite broad. Although neuromuscular disorders are the most common causes of generalized weakness, a thorough evaluation is necessary to delineate the underlying cause of weakness. Biochemical studies, neuroimaging, and electrophysiologic studies help to delineate most of the common disorders associated with weakness. Prompt identification of a neurologic disorder and initiation of therapy speeds up recovery and reduces
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