With a Stroke, Discerning ‘Mimic’ from ‘Chameleon’ Can Save a Life

The presentation of stroke can be complex, characterized by both false positives and false negatives. In the article “Strokes: Mimics and Chameleons” Fernandes et al address stroke-related diagnostic challenges.¹ “Mimics” (false positives)—ie, non-stroke conditions that present with symptoms similar to stroke—account for up to 25% of suspected stroke presentations. A “chameleon” is a stroke that masquerades as a different disease state (false negative);¹ indeed, a “seemingly infinite number” of ostensibly different clinical syndromes can turn out to be stroke.²

Despite the availability of measurement scales such as the Face, Arm, Speech, Time (FAST) score,³ or the Recognition of Stroke in the Emergency Room (ROSIER),⁴ diagnosis can remain elusive.¹ Moreover, sophisticated imaging techniques—eg, magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) and brain computed tomography (CT)—are sensitive and specific for diagnosing stroke, but their utility declines with time following stroke onset. Therefore, the authors recommend clinical history and examination as the “reference standard,” supported by brain imaging for avoiding both mimics and chameleons.

Stroke Mimics

Key diagnostic clues aid in detecting potential mimics.

Postictal Todd’s paresis, which accounts for almost 20% of stroke mimics, can be recognized by recurrent (albeit subtle) focal motor seizures, a history of epilepsy (often previously undiagnosed), or an old stroke that may have served as the substrate for the current seizure. MRI with DWI and apparent diffusion coefficient sequences can help distinguish remote from recent ischemic stroke. This is a critical distinction, as thrombolytic therapy is contraindicated in seizures.

Hypoglycemia accounts for a surprising number of stroke mimics. Although it commonly presents with autonomic symptoms, it can present with focal neurological symptoms and signs alone. Measuring blood sugar before administration of thrombolysis [ie, the “airway, breathing, circulation, don’t ever forget blood glucose” (ABC-DEFG) approach] is important.

Sepsis accounts for 12% of mimics. Systemic examination, together with septic screen, may identify the focus of infection. Fever and elevated inflammatory markers are important clues. Sepsis and stroke can occur simultaneously, or systemic upset may exacerbate neurological deficits from previous stroke. The authors advise establishing a clear history of previous strokes, residual neurological deficits, full drug history, and a history of sepsis symptoms.