512 - Anchoring Bias: Delayed Diagnosis of Myasthenia Gravis

Case Diagnosis: Myasthenia Gravis

Case Description:
A 45-year-old male presented with progressive muscle weakness and ptosis. Imaging revealed an incidental meningioma, leading to the attribution of his symptoms to the tumor. No further neuromuscular evaluation was conducted, and surgical intervention was deferred. The patient was admitted to an inpatient rehabilitation unit for functional decline. During his stay, a physiatrist performed a detailed physical examination, revealing patterns of weakness and fluctuating ptosis suggestive of a neuromuscular disorder. Subsequent diagnostic testing, including acetylcholine receptor antibody assays, confirmed a diagnosis of myasthenia gravis.


Discussions: Anchoring bias, a cognitive error where clinicians fixate on an initial diagnosis and overlook conflicting evidence, played a significant role in delaying the diagnosis in this case. The incidental finding of a meningioma led to an initial misattribution of the patient’s symptoms. Although proximal muscle weakness and wavering ptosis are characteristic of myasthenia gravis, their overlap with neurological symptoms from the brain lesion resulted in diagnostic anchoring. The delay in diagnosing myasthenia gravis underscores the risks of anchoring bias, especially when incidental findings are present. The neurosurgical evaluation may have submitted this patient to unnecessary surgical intervention. Additionally, delaying treatment in a myasthenic crisis may have resulted in permanent morbidity or mortality. Only after a comprehensive evaluation in the rehabilitation unit was the correct diagnosis considered, highlighting the need for persistent diagnostic vigilance.

Conclusions:
This case exemplifies how anchoring bias can delay the diagnosis of conditions such as myasthenia gravis. Prematurely attributing symptoms to an incidental meningioma obscured the accurate diagnosis and delayed appropriate treatment. Clinicians should maintain an open diagnostic approach and remain receptive to alternative explanations when initial findings do not fully explain the patient’s condition, to avoid cognitive errors and enhance patient care.