Time-dependent test characteristics of neck stiffness in patients suspected of nontraumatic subarachnoid haemorrhage

Background: Neck stiffness can be the only diagnostic clue for subarachnoid haemorrhage (SAH) at neurological examination in patients with a clinical suspicion of nontraumatic SAH who present with a normal level of consciousness and no focal neurologic deficits. Since the clinical impression is that neck stiffness may take several hours to develop, we determined time-dependent test characteristics of neck stiffness. Methods: We retrieved the presence of neck stiffness from the medical records of consecutive patients presenting between 2005 and 2013 with a clinical suspicion of SAH, a normal level of consciousness and no focal neurologic deficits. Test characteristics with corresponding 95% confidence intervals (CIs) were calculated for the evaluation of neck stiffness ≤. 6. h and 6-72. h after symptom onset for the diagnosis of nontraumatic SAH. In a secondary analysis, multiple imputation was used to account for missing values. Results: 114 of 247 included patients were diagnosed with nontraumatic SAH. Neck stiffness at neurological examination performed ≤. 6. h after symptom onset had a positive predictive value (PPV) of 90% (95% CI: 78%-97%) and negative predictive value (NPV) of 69% (95% CI: 59%-78%). Between 6 and 72. h after symptom onset the PPV was 76% (95% CI: 58%-89%) and NPV 91% (95% CI: 78%-98%). Multiple imputation to account for missing values yielded similar results. Conclusion: In patients with a normal level of consciousness without focal neurologic deficits the presence of neck stiffness is helpful but not pathognomic for the diagnosis of SAH. Moreover, the absence of neck stiffness does not rule out SAH, especially when evaluated ≤. 6. h after symptom onset.