Medical assistance is called for overhead during your flight to Hawaii. A 75-year-old man has fallen in the aisle after attempting to walk back to the restrooms. History is obtained from the son who accompanies him. He recalls a history of diabetes and hypothyroidism. The patient is returning home after visiting family and is being evaluated by a prominent dementia specialist. The son cannot name a diagnosis but remembers that a recent MRI revealed “enlarged chambers.” The patient is mumbling about having successfully made it to the restroom five times during this flight.
Which of the following is the most likely diagnosis?
Correct Answer: C
Limited information is provided in the stem to make a definitive diagnosis. Key pieces include presumed dementia, gait instability, frequent urination, and an MRI suggestive of ventriculomegaly. These fit the classic triad of NPH (C). Diagnosis is usually aided by cognitive evaluation, MRI, lumbar puncture, and ruling out other causes of gait and urinary dysfunction. Peripheral neuropathy may explain gait and urinary problems with his history of diabetes but likely would not explain the MRI and cognitive findings (D). Alcohol intoxication may explain frequent trips to the restroom and an unstable gait; however, this would be an unlikely explanation for his chronic problems (A).
The differential for dementia should include Alzheimer and Parkinson disease. In fact, Alzheimer dementia is more common than NPH overall. Gait impairment and urinary incontinence can coexist in patients with Alzheimer disease; however, they are usually explained by other causes. Characteristically, dementia precedes these findings in Alzheimer disease (B). Parkinson disease can present with dementia later in the disease course. Distinguishable motor findings are typically present including tremor, bradykinesia, and rigidity but can manifest as gait instability and urinary incontinence (E). Again, the presence of ventriculomegaly makes NPH more likely than these causes of dementia.
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A 49-year-old woman requires endotracheal intubation for declining neurologic status. Airway is secured promptly with a rapid sequence induction of ketamine 150 mg and succinylcholine 140 mg. The neurosurgeon on call is on the phone wanting an explanation of why the intracranial pressure (ICP) has elevated to 27 mm Hg.
What are the anticipated physiologic effects of ketamine?
Correct Answer: B
Ketamine is an NMDA receptor antagonist that provides dissociative effects and can be used to provide rapid anesthesia in intubation scenarios, with dosing typically 1 to 2 mg/kg IV. When used as a sole induction agent, it may increase cerebral blood flow and ICP by virtue of sympathetic stimulation (B). This effect has traditionally warranted the use of other anesthetics in patients with concern for intracranial hypertension. Sympathetic stimulation also preserves or increases mean arterial pressure following induction, provided that the patient’s catecholamine stores are not depleted. Other notable effects include bronchodilation and unpleasant dreams.
A 34-year-old man suffers blunt head trauma during a basketball game in prison. Imaging reveals large right suboral hematoma with 8 mm midline shift. The patient is intubated; his eyes do not open to stimulus; he has no verbal response; and limbs extend to painful stimulus. He has fixed dilated pupils.
Which of the following regarding uncal herniation is TRUE?
Expanding mass lesions in the brain can lead to lateral and downward displacement of the brain. Horizontal shifts of midline structures >8 mm are associated with impaired consciousness and shifts >11 mm are typically consistent with coma. In uncal herniation syndrome, lateral forces lead to asymmetric herniation of the temporal uncus. The ipsilateral oculomotor nerve (CN III) is displaced and stretched, leading to pupillary dilation, downward and outward eye deviation (C).
Subsequently, contralateral pupil reactivity may be lost with midbrain damage (B). Hemiplegia occurs with compression of the corticospinal tract, not the spinothalamic tract (D). Vestibulo-ocular reflexes are present and normal early until brainstem compression occurs (E). Clinically, these patients develop signs of elevated ICP as identified in the Cushing triad (hypertension, bradycardia, irregular respirations). Papilledema is consistent with ICP elevation but not a part of the triad (A).
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