In a 77-year-old assisted‑living resident found in bed unable to speak with a normal head CT, what other causes could explain the acute aphasia/mutism?

Differential Diagnosis for Acute Mutism in a 77-Year-Old with Normal Head CT

In a 77-year-old assisted-living resident found unresponsive and unable to speak with a normal head CT, the most likely causes are metabolic/infectious delirium, post-ictal state, medication toxicity, or stroke in a CT-negative location—and MRI brain should be obtained urgently if initial metabolic workup is unrevealing. 1, 2, 3

Immediate Life-Threatening Causes to Exclude First

• Hypoglycemia or severe hyperglycemia must be checked immediately with point-of-care glucose testing, as these are among the most common reversible causes of acute altered mental status 3
• Severe electrolyte abnormalities (hyponatremia, hypernatremia, hypercalcemia) can rapidly cause altered consciousness and mutism 3
• Hypoxia from respiratory failure requires immediate pulse oximetry and assessment 3
• Hypothermia can precipitate profound altered mental status in elderly patients 3

Neurological Causes Despite Normal CT

Acute Stroke (CT-Negative)

• Small lacunar infarcts can present with altered mental status without focal deficits and may not be visible on initial CT 3, 4
• Posterior circulation strokes (brainstem, thalamus) are frequently missed on CT and can present with isolated mutism or decreased responsiveness 1
• Notably, 70% of patients with missed ischemic stroke diagnoses presented with altered mental status rather than classic focal deficits 2
• MRI brain is significantly more sensitive than CT for detecting acute ischemia and should be obtained when stroke remains suspected despite negative CT 1, 2

Post-Ictal State

• Non-convulsive status epilepticus can present as prolonged unresponsiveness or mutism without witnessed seizure activity 3
• Post-ictal confusion can last hours and mimic other causes of altered mental status 3
• Consider EEG if patient remains unresponsive beyond expected timeframe for metabolic causes 3

Other Neurological Considerations

• Subdural hematoma from unrecognized trauma, especially if on anticoagulation, though this should be visible on CT 3
• Encephalitis (viral, autoimmune) requires high clinical suspicion and is better detected on MRI than CT 1, 2

Infectious Causes (Most Common in Elderly)

• Urinary tract infection is the most common infectious precipitant of delirium in elderly patients 3
• Pneumonia can present with isolated altered mental status without respiratory symptoms 3
• Meningitis or encephalitis should be considered if fever, neck stiffness, or other signs present—lumbar puncture is preferred over CT as initial diagnostic test 2
• Sepsis from any source was the leading cause of altered mental status (29.1%) in one large study of elderly patients 5

Medication/Toxicologic Causes

• Polypharmacy is a major contributor to delirium in assisted-living residents 3
• Anticholinergic medications (antihistamines, tricyclic antidepressants, bladder medications) commonly cause acute confusion and decreased responsiveness 3
• Sedatives and benzodiazepines can accumulate in elderly patients with reduced clearance 3
• Opioid toxicity should be considered, especially if respiratory depression present 3
• Review all recent medication changes, over-the-counter medications, and supplements 3

Metabolic/Endocrine Causes

• Thyroid disorders (severe hypothyroidism/myxedema coma or thyrotoxicosis) can present with profound altered mental status 3
• Adrenal insufficiency (Addisonian crisis) can cause acute decompensation 3
• Hepatic encephalopathy if underlying liver disease present 6
• Uremia from acute or chronic kidney disease 3
• Severe vitamin deficiencies (thiamine/Wernicke encephalopathy, B12) may show characteristic MRI findings 1

Psychiatric/Functional Causes

• Catatonia from severe depression or other psychiatric illness can present as mutism and unresponsiveness 3
• Severe depression with psychomotor retardation may mimic neurological causes 3
• Conversion disorder is a diagnosis of exclusion after organic causes ruled out 3

Diagnostic Algorithm Based on Guidelines

Step 1: Immediate Bedside Assessment

• Point-of-care glucose, vital signs including temperature, pulse oximetry 3
• Focused neurological examination looking specifically for:
  • Focal deficits (even subtle asymmetry) 2, 7, 4
  • Pupillary responses and eye movements 2
  • Level of consciousness (Glasgow Coma Scale) 2, 5
  • Signs of trauma or head injury 2, 7

Step 2: Initial Laboratory Workup

• Comprehensive metabolic panel (electrolytes, renal function, calcium, glucose) 1, 3
• Complete blood count (infection, anemia) 1, 3
• Thyroid function tests (TSH at minimum) 1, 3
• Urinalysis and culture 1, 3
• Chest X-ray if respiratory symptoms or hypoxia 3
• Blood cultures if fever or sepsis suspected 3
• Medication levels if on digoxin, anticonvulsants, or other drugs with narrow therapeutic windows 3

Step 3: When to Obtain MRI Brain

MRI should be obtained urgently if: 1, 2

• Initial metabolic/infectious workup is unrevealing after 24-48 hours 2
• Clinical suspicion for stroke remains high despite negative CT 1, 2
• Any focal neurological findings develop 2
• Patient has known malignancy (evaluate for metastases) 1, 2
• Suspected encephalitis or meningitis 1, 2

MRI changed clinical management in 76% of ICU patients with acute disorders of consciousness, including revised diagnoses in 20% and changes in level of care in 21% 2

Critical Clinical Pitfalls to Avoid

• Do not assume delirium is benign—mortality doubles when delirium diagnosis is missed, and overall mortality in altered mental status patients is 8.1% 3
• Normal CT does not exclude stroke—small lacunar infarcts and posterior circulation strokes are frequently CT-negative 1, 2, 3
• Absence of fever does not exclude infection—elderly patients often have blunted fever response 3
• Do not attribute altered mental status to "old age" or dementia without thorough evaluation—this represents an acute change requiring explanation 1, 3
• Anticoagulation alone is not predictive of positive CT findings (OR 1.2, not significant) in the absence of trauma or focal deficits 8

Prognostic Context

• In elderly patients with altered mental status and normal CT, acute findings on neuroimaging occur in only 1.7%-6.4% when high-risk features are absent 2, 5
• However, 15.6% of elderly ED patients with confusion have abnormal head CT overall 8
• Focal neurological deficits are the strongest predictor of positive neuroimaging (OR 101.8) 8
• The diagnostic yield of CT is very low (4.7%) in delirium without focal deficits, GCS <14, or trauma 7