Stroke mimic: Perfusion magnetic resonance imaging of a patient with ictal paralysis.

We present an uncommon case of clinically diagnosed window period stroke subsequently recognised on diffusion - perfusion MRI as ictal paralysis due to focal inhibitory seizures or negative motor seizures. This case highlights the importance of MRI with perfusion imaging in establishing the diagnosis of stroke mimics and avoiding unnecessary thrombolysis.

Introduction

Mimics account for approximately one of five clinically diagnosed acute strokes.[1] Results of the European Cooperative Acute Stroke Study II showed 17% of patients who received thrombolytic therapy were stroke mimics.[2] Plain computed tomography (CT) is considered the standard of care in the assessment of window period stroke. However, its primary purpose in acute stroke is to rule out hemorrhage, a potential contraindication for thrombolysis. A CT scan often fails to identify stroke mimics such as ictal or postictal paralysis, migraine, hysteria, hypoxic hemiplegia, and hypoglycemia.[345] As CT is normal in these patients who clinically mimic stroke; in the absence of hemorrhage, they are sometimes treated with expensive, unnecessary, and potentially harmful intravenous (IV) thrombolysis.

Case Report

A 50-year-old female presented with sudden inability to speak, deviation of angle of mouth, and dropping of objects with the right hand. On examination, she was confirmed as globally aphasic with right facial palsy and hemiplegia (Power 0). Deficit onset was less than an hour. She was diagnosed as acute window period stroke, the National Institute of Health Stroke Scale was documented as 17 and as per our institute's stroke protocol, she was immediately shifted for magnetic resonance imaging (MRI). However, a diffusion-weighted image (DWI) showed no focal area of low apparent diffusion coefficient/no acute infarct [Figure 1a and b]. Fluid-attenuated inversion recovery images [Figure 1c] were also normal. Time of flight angiography showed patent arteries. In view of persistent deficit in the absence of diffusion abnormality, a perfusion study was obtained, which showed significant focal hyperperfusion in the left parietal parenchyma. Focal elevation of cerebral blood volume and flow (CBV and CBF) and reduction of mean transit time were observed [Figure 2]; leading to diagnosis of hyperperfusion of ictal paralysis. Delayed contrast T1-images showed no focal structural lesion. In view of diagnosis of stroke mimic (ictal paralysis), IV thrombolysis was deferred. Complete recovery was observed in few hours and electroencephalograph on day 2 was normal.

Figure 1

(a) Diffusion-weighted and (b) apparent diffusion coefficient images show no area of cytotoxic edema. (c) Fluid-attenuated inversion recovery image is normal

Figure 2

(a) Cerebral blood flow and (b) cerebral blood volume maps of magnetic resonance imaging perfusion study show focal hyperperfusion (white arrows). (c) Mean transit time is reduced (black arrows)

Discussion

Stroke mimics constitute 5%–30%[5] of clinically diagnosed strokes. CT, although a standard of care, may miss diagnosis of stroke mimics leading to unnecessary thrombolysis. Our case highlights the importance of MRI in acute stroke to avoid unnecessary thrombolysis. DWI in this patient presenting with aphasia and hemiplegia was negative for cytotoxic edema thus ruling out an infarct. Localized hyperperfusion in the presence of focal neurological deficit established diagnosis of ictal paralysis. We completed the study with contrast T1 to rule out structural abnormality. If the same patient were to have been assessed solely with CT, findings of normal parenchyma without hemorrhage would have led to IV thrombolysis and subsequent deficit recovery incorrectly attributed to successful reperfusion.

There are two theories to explain this clinical presentation in context of our radiological findings. The first postulate is the deficit represented postictal (Todds) paralysis.[6] Todds paralysis or epileptic hemiplegia is a transient paralysis following motor seizures. This diagnosis was unlikely as perfusion showed increased focal CBF and CBV; whereas postictal paralysis has been correlated with hypoperfusion due to metabolic exhaustion of focus area following convulsions. The second, more likely postulate is that of ictal paralysis related to negative motor seizure (NMS). NMS is an uncommon epileptic condition presenting as motor arrest or inability to conduct voluntary movements (praxis).[7] Ictal paralysis is a negative ictal phenomenon that electrically corresponds to activation of the negative motor areas.[8] Paucity of clinically apparent convulsions in our case was likely due to origin of seizures from the negative motor areas.

Although CT is fast, economical and widely available, CT-based incorrect thrombolysis may eventually be expensive; considering high cost of unnecessary treatment in a stroke mimic and an increased risk of symptomatic hemorrhage in a large infarct not demonstrated on CT. It is universally accepted that CT is significantly inaccurate in measuring infarct size as compared to diffusion MRI. The superiority of MRI in diagnosing acute stroke is well-documented.[9] Underestimation of infarct core size on CT may lead to thrombolysis in large infarcts and increased incidence of symptomatic hemorrhage and mortality.

The most sensitive imaging biomarker of response to reperfusion therapies is the size of initial infarct on DWI. DWI infarct volume is considered the best predictor of clinical outcome (efficacy) as well as symptomatic hemorrhagic transformation and mortality (safety) after treatment. DWI core of more than 70 ml is the strongest imaging biomarker of poor outcome. In the recent years, few small phase 2 trials have established the superiority of MRI in guiding thrombolysis within and beyond the 3 h interval. They have established the precedence of MRI-based protocols in improving safety with regard to mortality due to symptomatic intracranial hemorrhage and efficacy in the form of better treatment outcome. This paper adds to the growing body of evidence on the superiority of MRI in improving safety and efficacy of reperfusion in acute strokes and particularly to avoid unnecessary thrombolysis in stroke mimics. Its eventual use in lieu or addition to a CT will need to await evidence from pharmacoeconomic studies.

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Conflicts of interest

There are no conflicts of interest.