Cranial computed tomography before lumbar puncture - A prospective clinical evaluation

Objective: To prospectively identify which patients can safely undergo lumb ar puncture (LP) without screening cranial computed tomography (CT). Methods: Emergency department physicians examined patients before CT. Exami ners recorded the presence or absence of 10 clinical findings and answered 8 additional questions. The criterion standard was noncontrast cranial CT i nterpreted by staff radiologists. Clinical findings were prospectively comp ared with those of CT. Results: One hundred thirteen consecutive adults with the urgent need for L P (median age, 42 years) were studied. Fifteen percent of patients meeting entrance criteria had new CT-documented lesions; with 2.7% having lesions t hat contraindicated LP. Sensitivity, specificity, and likelihood ratios (LR s) were measured for the clinical findings. Three statistically significant predictors of new intracranial lesions were identified: altered mentation (positive LR, 2.2; 95% confidence interval [ CI], 1.5-3.2), focal neurologi c examination (positive LR, 4.3; 95% CI, 1.9-10), and papilledema (positive LR, 11.1; 95% CI, 1.1-115). No single item adequately predicted the absenc e of CT abnormalities, but the clinical screening items in aggregate signif icantly predicted the results (negative LR, 0; upper 95% confidence limit, 0.6). The overall clinical impression had the highest predictive value in i dentifying patients with CT-defined contraindications to LP (positive LR, 1 8.8; 95% CI, 4.8-43). Conclusions: Because of the low prevalence of lesions that contraindicate L P, screening cranial CT solely to establish the safety of performing an LP typically provides limited additional information. Physicians can use their overall clinical impression and 3 clinical predictors to identify patients with the greatest risk of having intracranial lesions that may contraindic ate LP.