Accuracy of NIH Stroke Scale for diagnosing aphasia

Objectives

The National Institutes of Health Stroke Scale (NIHSS) has not been validated to diagnose aphasia in the stroke population. We therefore examined the diagnostic accuracy of NIHSS for detecting aphasia in acute ischemic stroke.

Methods

Consecutive patients with acute first‐ever ischemic stroke were included prospectively in Lund Stroke Register Study at Skåne University Hospital, Sweden. Exclusion criteria were: (a) non‐native Swedish; (b) obtundation (c) dementia or psychiatric diagnosis. Patients were assessed with NIHSS item 9 (range 0–3, where 1–3 indicate aphasia) by a NIHSS certified research nurse in the acute phase after stroke onset (median 3 days). Within 24 h after this assessment, a speech therapist evaluated the patients’ language function with the comprehensive language screening test (LAST, range 0–15 where 0–14 indicates aphasia). Data were analyzed using LAST as ‘reference standard’.

Results

We examined 221 patients. Among these, 23% (n = 50) had aphasia according to NIHSS (distribution of scores 0, 1, 2, 3 were n = 171, n = 29, n = 12, n = 9) compared to 26% (n = 58) with aphasia according to LAST (score ≤14; median = 11). Assuming LAST as reference standard, NIHSS gave 16 false negatives (NIHSS item 9 = 0) for aphasia (LAST scores range 8–14), and 8 false positives (NIHSS item 9 score = 1) for aphasia, yielding a sensitivity of 72% (0.59–0.83) and a specificity of 95% (0.91–0.98).

Conclusions

When using NIHSS for screening and diagnosing aphasia in adults with acute ischemic stroke, patients with severe aphasia can be detected, however, some mild aphasias might be misclassified. Given the 72% sensitivity, absence of aphasia on the NIHSS should not be used to guide stroke treatment.

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