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Difficulty: HardOrdering Laboratory Tests

Evaluate the following clinical vignettes of patients presenting with diverse manifestations of muscle weakness. Match each clinical scenario with the most specific targeted serologic laboratory test indicated to establish the diagnosis.

  • A 48-year-old woman presents with progressive difficulty climbing stairs and rising from a seated position. Physical examination reveals a violaceous periorbital rash and flat-topped, erythematous papules over her metacarpophalangeal joints.Anti-Jo-1 (histidyl-tRNA synthetase) and anti-Mi-2 autoantibodies
  • A 34-year-old man reports intermittent double vision and drooping of his eyelids that typically becomes more pronounced in the late afternoon. Pupillary responses to light and accommodation are fully preserved.Anti-acetylcholine receptor (AChR) binding autoantibodies
  • A 62-year-old man with a 40-pack-year smoking history develops proximal muscle weakness and generalized xerostomia. Neurologic examination shows reduced deep tendon reflexes that temporarily normalize following brief maximal voluntary muscle contraction.Anti-voltage-gated calcium channel (VGCC) autoantibodies
  • A 58-year-old woman presents with severe, progressive proximal myopathy and elevated creatine kinase levels that have continued to worsen despite the cessation of her prescribed rosuvastatin therapy four months prior.Anti-3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase autoantibodies

Answer

Dermatomyositis pairs with Anti-Jo-1/Mi-2; Myasthenia Gravis pairs with Anti-AChR; Lambert-Eaton Myasthenic Syndrome pairs with Anti-VGCC; and Statin-induced immune-mediated necrotizing myopathy pairs with Anti-HMG-CoA reductase autoantibodies.
Each correct pairing accurately links a classic clinical presentation of an autoimmune neuromuscular disease with its gold-standard confirmatory serologic test. Dermatomyositis is confirmed via myositis-specific antibodies (Jo-1, Mi-2). Myasthenia gravis is confirmed by AChR antibodies. Lambert-Eaton myasthenic syndrome is confirmed via VGCC antibodies. Statin-induced immune-mediated necrotizing myopathy is confirmed via HMG-CoA reductase antibodies.

Step-by-Step Solution

1
Analyze the clinical features of each vignette to identify the specific neuromuscular syndrome.
The vignettes describe dermatomyositis, myasthenia gravis, Lambert-Eaton myasthenic syndrome, and statin-induced immune-mediated necrotizing myopathy, respectively.
Accurate clinical pattern recognition is required before selecting the appropriate confirmatory serologic test.
2
Select the confirmatory serology for the 48-year-old with rash and proximal weakness.
Match with Anti-Jo-1 and anti-Mi-2 autoantibodies.
These are specific myositis-associated autoantibodies utilized in the diagnostic workup of dermatomyositis.
3
Select the confirmatory serology for the 34-year-old with fatigable ocular weakness.
Match with Anti-acetylcholine receptor (AChR) binding autoantibodies.
AChR antibodies are the initial and most specific diagnostic laboratory test for myasthenia gravis.
4
Select the confirmatory serology for the 62-year-old smoker with areflexia that improves with use.
Match with Anti-voltage-gated calcium channel (VGCC) autoantibodies.
Lambert-Eaton myasthenic syndrome is a paraneoplastic syndrome (often small cell lung cancer) mediated by anti-VGCC antibodies.
5
Select the confirmatory serology for the 58-year-old with progressive statin-associated weakness after drug cessation.
Match with Anti-HMG-CoA reductase autoantibodies.
Unlike self-limiting statin myopathy, progressive weakness despite cessation indicates an immune-mediated process confirmed by this specific antibody.

Key Concept

Selecting the most appropriate targeted autoantibody testing panels based on the specific clinical features of inflammatory myopathies and neuromuscular junction disorders.
Estimated Time:2m 0s
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Ordering Laboratory Tests

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