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Difficulty: HardDiagnostic Workup and Test Sequencing

A 68-year-old retired architect is brought to the clinic by his husband due to a 14-month history of progressive cognitive changes. The husband reports that the patient frequently misplaces household items, repeats questions in conversation, and recently struggled to complete their annual tax return—a task he previously managed with ease. The patient has a medical history of essential hypertension and hyperlipidemia, both well-controlled on lisinopril and atorvastatin. Vital signs are within normal limits. A complete blood count and comprehensive metabolic panel obtained during a health fair one month ago were completely normal, with no evidence of anemia or electrolyte derangements. Neurological examination shows normal cranial nerves, strength, and reflexes, and his gait is steady. A Montreal Cognitive Assessment (MoCA) is performed, and the patient scores 21/30, losing points primarily on delayed recall and visuospatial tasks. Along with a comprehensive history and physical examination, which of the following tests should be ordered as part of the complete set of initial concurrent diagnostic workup? (Select 3)

  1. Magnetic resonance imaging of the brain without contrastAnswer
  2. Measurement of serum vitamin B12 levelAnswer
  3. C
    Positron emission tomography of the brain with fluorodeoxyglucose
  4. D
    Lumbar puncture for cerebrospinal fluid Alzheimer disease biomarkers
  5. Measurement of serum thyroid-stimulating hormoneAnswer

Answer

The correct initial concurrent diagnostic tests are magnetic resonance imaging of the brain without contrast, measurement of serum vitamin B12 level, and measurement of serum thyroid-stimulating hormone.
The initial diagnostic workup for a patient with suspected major neurocognitive disorder (dementia) focuses on identifying potentially reversible causes and establishing a baseline of brain anatomy. Guidelines mandate concurrent testing with a serum thyroid-stimulating hormone (TSH) to evaluate for hypothyroidism and a serum vitamin B12 level to rule out deficiency-related cognitive impairment. Notably, a normal complete blood count does not exclude B12 deficiency, as neurologic manifestations frequently occur in the absence of macrocytic anemia. Additionally, structural neuroimaging is required. Magnetic resonance imaging (MRI) of the brain without contrast is the preferred initial imaging modality to assess for cerebrovascular disease, subdural hematomas, normal pressure hydrocephalus, mass lesions, and patterns of regional atrophy (e.g., medial temporal lobe atrophy).

Step-by-Step Solution

1
Analyze the clinical presentation and temporal course.
The patient exhibits insidious, progressive cognitive decline primarily affecting memory and executive function (major neurocognitive disorder), without focal neurologic deficits.
Establishing the broad clinical syndrome determines the standardized diagnostic pathway.
2
Identify guideline-concordant initial diagnostic tests for dementia.
Routine initial workup requires evaluating for reversible causes and structural lesions through targeted labs (TSH, Vitamin B12) and structural neuroimaging (MRI).
B12 deficiency and hypothyroidism are common, reversible causes of cognitive impairment. Structural brain disease (e.g., occult strokes, tumors) must be ruled out.
3
Differentiate mandatory initial screening from advanced, subsequent diagnostic testing.
Advanced metabolic imaging (PET) and invasive testing (lumbar puncture) are excluded from the initial concurrent workup.
These advanced tests represent incorrect test sequencing if ordered immediately; they are strictly reserved for cases with atypical presentations, early onset, or diagnostic ambiguity following standard evaluation.

Key Concept

The initial diagnostic workup for neurocognitive decline requires concurrent evaluation for structural brain lesions (via MRI or CT) and reversible metabolic etiologies (via serum TSH and Vitamin B12) prior to utilizing advanced imaging or invasive biomarker testing.
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Diagnostic Workup and Test Sequencing

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