Failure to accurately assess optic nerve drives IIH overdiagnosis

By Lucy Piper, Senior medwireNews Reporter

Researchers put overdiagnosis of idiopathic intracranial hypertension (IIH) down to inaccurate ophthalmoscopic examination in headache patients and wrongly suspecting the condition in young obese women with headaches.

The team found that among 86 patients with an IIH diagnosis referred over an 8-month period to one neuro-ophthalmology service at a tertiary centre, IIH was misdiagnosed in 39.5%.

The main reasons for this, according to the Diagnosis Error Evaluation and Research tool, were failure to appreciate or misinterpretation of a physical examination finding in 67.6% of patients and errors in assessment, specifically bias to an IIH diagnosis without due weight given to other possibilities, in 17.6% of patients.

In the case of physical examination findings, the ocular fundus was often misinterpreted in obese headache patients, the team reports, noting that in 20% of patients with headaches an IIH diagnosis was given without an ophthalmoscopic examination.

The majority of those misdiagnosed were women with an average age of 38 years and an average body mass index of 34.9 kg/m².

The researchers comment in Neurology that wrongly suspecting IIH in such women is unsurprising for emergency department providers or primary care physicians, but they note that most misdiagnoses were made by optometrists, ophthalmologists and neurologists who should be comfortable examining and evaluating the optic nerve.

“Subconscious and intuitive processes led these providers to overdiagnose IIH because the patients were young obese women; this characteristic pushed the care providers into cognitive errors by the succession of fixed-action patterns”, say Valerie Biousse (Emory University School of Medicine, Atlanta, Georgia, USA) and fellow researchers.

As a consequence of misdiagnosis, 33.7% of patients received unnecessary tests, 31.4% underwent unnecessary invasive procedures and 9.3% had diagnoses requiring further investigation that went undetected.

The researchers also found that among an additional 79 patients referred to rule out possible IIH, only 19 were confirmed as having IIH. And of these, just one was referred because of an apparently abnormal optic nerve, emphasizing the difficulty faced by physicians in reliably diagnosing or ruling out papilledema in headache patients, they say.

“It is possible that one way to improve this deficiency is to encourage clinicians to use nonmydriatic retinal fundus photography”, say Biousse et al.

This is seconded by Steven Galetta (New York University School of Medicine, USA) and Kathleen Digre (University of Utah School of Medicine, Salt Lake City, USA) in a related editorial, believing it should be “widely adopted, and may now even enable use with handheld/smartphone applications, which enable a dynamic view of the ocular fundus by a video feed.”

And with the emergence of telemedicine, such approaches could make neuro-ophthalmologists and other experts in ophthalmoscopy more available to practicing neurologists, they add, although they conclude that “fundus interpretation will continue to require basic clinical expertise that ultimately trumps technology.”

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