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Difficulty: Very hardOrdering Laboratory Tests

Match each complex neurological or paraneoplastic clinical presentation with the most specific and appropriate targeted diagnostic laboratory test.

  • An otherwise healthy 62-year-old female patient is evaluated for a three-month history of rapidly progressive memory loss, exaggerated startle response (myoclonus), and gait instability. Electroencephalogram reveals 1-Hz generalized periodic sharp wave complexes.Cerebrospinal fluid real-time quaking-induced conversion (RT-QuIC) assay
  • Two months following resection of an ovarian teratoma, a 26-year-old female patient develops acute severe psychiatric disturbances, prominent orofacial dyskinesias, and subsequent autonomic instability requiring intensive care.Cerebrospinal fluid analysis for anti-GluN1 (NMDA) receptor IgG antibodies
  • A 68-year-old male with a 40-pack-year tobacco use history exhibits subacute onset of severe dysarthria and appendicular ataxia. Initial chest radiography raises high suspicion for a central lung malignancy.Serum panel for anti-Hu (ANNA-1), anti-Yo (PCA-1), and anti-Ri (ANNA-2) antibodies
  • Following a documented episode of bacterial gastroenteritis, a 45-year-old male develops acute bilateral ophthalmoplegia, significant gait ataxia, and diffuse areflexia without prominent limb weakness.Serum testing for anti-GQ1b ganglioside antibodies

Answer

The correct pairings match the underlying syndrome to its specific diagnostic assay: Creutzfeldt-Jakob disease pairs with the RT-QuIC assay; Anti-NMDA receptor encephalitis pairs with anti-GluN1 receptor antibodies; Paraneoplastic cerebellar degeneration pairs with the anti-Hu/Yo/Ri panel; and Miller Fisher syndrome pairs with anti-GQ1b ganglioside testing.
Each clinical vignette presents a highly specific neurological autoimmune or rapidly progressive degenerative syndrome that corresponds uniquely to a specialized diagnostic laboratory test. Properly ordering these tests prevents diagnostic delay and premature closure in rare but critical conditions.

Step-by-Step Solution

1
Evaluate the presentation of the 62-year-old with rapidly progressive dementia and myoclonus.
Identifies highly suspected Creutzfeldt-Jakob disease.
The clinical triad combined with 1-Hz sharp wave complexes on EEG requires specific confirmation of prion disease via the RT-QuIC assay.
2
Analyze the 26-year-old with post-teratoma psychiatric symptoms and dyskinesias.
Identifies anti-NMDA receptor encephalitis.
Ovarian teratomas commonly trigger NMDA receptor autoantibodies, requiring specific cerebrospinal fluid testing for confirmation.
3
Assess the 68-year-old smoker with subacute cerebellar ataxia and a lung mass.
Identifies paraneoplastic cerebellar degeneration.
Suspected small cell lung cancer driving an autoimmune cerebellar process necessitates a paraneoplastic antibody panel (including anti-Hu).
4
Examine the 45-year-old with acute ophthalmoplegia, ataxia, and areflexia post-gastroenteritis.
Identifies Miller Fisher syndrome.
This specific clinical triad (without generalized weakness) is universally linked to anti-GQ1b antibodies, differentiating it from classic Guillain-Barré syndrome.

Key Concept

Targeted laboratory evaluation of rapidly progressive neurological and paraneoplastic syndromes based on highly specific clinical phenotypes.
Estimated Time:2m 0s
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Ordering Laboratory Tests

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