Neurology · Altered Mental Status
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Suspect it with altered mental status plus a flapping tremor (asterixis), hyperreflexia, and myoclonus in the setting of severe azotemia.
Typically occurs once BUN > 100 mg/dL in acute kidney injury or end-stage renal disease.
The definitive treatment is urgent hemodialysis to clear circulating uremic toxins; delaying dialysis risks irreversible neurologic damage.
EEG is the gold-standard adjunct, classically showing diffuse generalized slowing with theta and delta waves.
Focal neurologic deficits are notably absent, which helps distinguish it from acute stroke, but brain imaging is needed to exclude intracranial hemorrhage.
For uremic seizures use lorazepam or levetiracetam, and avoid valproic acid due to altered protein binding increasing free drug toxicity.
Distinguish from dialysis disequilibrium syndrome, which causes neurologic decline during or right after initial dialysis from rapid osmolar shifts.
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A 58-year-old man with end-stage renal disease who has missed his last two dialysis sessions is brought in confused and lethargic. On exam he has a coarse flapping tremor of the outstretched hands, hyperreflexia, and intermittent myoclonic jerks, but no focal deficits. Labs show BUN of 130 mg/dL, creatinine of 11 mg/dL, potassium of 6.1 mEq/L, and metabolic acidosis. A non-contrast head CT is unremarkable.
Which of the following is the most appropriate definitive treatment?
Urgent hemodialysis.
Altered mental status with asterixis and myoclonus in the setting of severe azotemia (BUN > 100) and a normal head CT points to uremic encephalopathy, whose definitive treatment is hemodialysis to clear retained toxins. Symptoms typically reverse within days of dialysis, whereas delaying it risks permanent neurologic injury.
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Etiology / Epidemiology
Occurs in acute kidney injury or end-stage renal disease due to retained uremic toxins, typically when BUN > 100 mg/dL.
Clinical Manifestations
Presents with altered mental status, flapping tremor known as asterixis, hyperreflexia, and myoclonus progressing to coma.
Diagnosis
Clinical diagnosis based on neurologic decline in the setting of severe azotemia, with EEG classically showing diffuse generalized slowing.
Treatment
The definitive treatment is urgent hemodialysis to clear circulating toxins; delaying dialysis risks irreversible neurologic damage.
Prognosis
Symptoms usually reverse completely within days of initiating dialysis, but untreated uremic encephalopathy is universally fatal.
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Epidemiology & Etiology
Develops in patients with severe acute or chronic renal failure, typically when the glomerular filtration rate (GFR) drops below 10 mL/min. The exact trigger is the accumulation of multiple uremic toxins, most notably guanidino compounds and parathyroid hormone. It is classically associated with a BUN > 100 mg/dL, though the rapid rate of BUN rise in acute kidney injury is more predictive of symptom onset than the absolute value.
Pertinent Anatomy
Uremic toxins readily cross the blood-brain barrier, causing diffuse cerebral dysfunction rather than focal neurologic deficits. The basal ganglia and cerebral cortex are highly susceptible to these metabolic derangements, producing the classic movement disorders and cognitive decline.
Pathophysiology
The accumulation of uremic toxins alters blood-brain barrier permeability and impairs cerebral oxygen utilization. Elevated parathyroid hormone (PTH) leads to increased intracellular calcium in brain tissue, which disrupts neurotransmission. Concurrently, retained toxins cause a neurotransmitter imbalance by downregulating GABA and upregulating glutamate. This cascade ultimately results in generalized cortical excitability and diffuse neuronal dysfunction.
Clinical Manifestations
Early signs include lethargy, irritability, and the classic flapping tremor known as asterixis. As toxicity progresses, patients develop hyperreflexia, myoclonus, and seizures. Cognitive decline fluctuates, often mimicking psychiatric disorders before progressing to profound stupor and coma. Focal neurologic deficits are notably absent, which helps differentiate this from acute stroke.
Diagnosis
Diagnosis is primarily clinical, requiring altered mental status in the presence of severe azotemia after excluding structural causes. Laboratory testing typically reveals a BUN > 100 mg/dL, alongside profound hyperkalemia and metabolic acidosis. Electroencephalogram (EEG) is the gold-standard diagnostic adjunct, classically demonstrating diffuse generalized slowing with prominent theta and delta waves. Brain imaging is mandatory to rule out intracranial hemorrhage but is otherwise unremarkable in pure uremia.
Treatment
The first-line treatment is immediate hemodialysis to clear the offending uremic toxins. Medical management of uremic seizures is challenging; lorazepam or levetiracetam are preferred, while renally cleared anticonvulsants must be strictly dose-adjusted. Avoid valproic acid due to altered protein binding in uremia, which increases free drug toxicity. Correction of concurrent metabolic emergencies, such as administering calcium gluconate for severe hyperkalemia, is critical while preparing for dialysis.
Prognosis
Neurologic symptoms typically improve within 24 to 48 hours of initiating hemodialysis. The EEG abnormalities usually normalize shortly after clinical improvement is observed. However, failure to initiate prompt dialysis leads to irreversible brain injury, progressive coma, and death.
Differential Diagnosis
1. Hepatic Encephalopathy: Also presents with asterixis but features elevated ammonia levels and signs of liver failure like caput medusae.
2. Hypertensive Encephalopathy: Driven by malignant hypertension and classically presents with papilledema on fundoscopy.
3. Wernicke Encephalopathy: Characterized by the Wernicke triad of confusion, ataxia, and ophthalmoplegia due to thiamine deficiency.
4. Dialysis Disequilibrium Syndrome: Presents with neurologic decline during or immediately after initial dialysis sessions due to rapid osmolar shifts causing cerebral edema.