Neuroleptic malignant syndrome (NMS) requires prompt recognition for effective management, but there are no established diagnostic criteria.

To validate the recently published international expert consensus (IEC) diagnostic criteria for NMS, which assign priority points based on the relative importance of each criterion for diagnosing NMS.

Determine optimal diagnostic cutoff for priority point score.

Data were extracted from 221 archived telephone contact reports of clinician-initiated calls to a national telephone consultation service from 1997–2009; each case was given a total priority point score based on the IEC criteria. DSM-IV-TR research criteria, in original form and modified to accept less than ‘severe’ rigidity, served as the primary diagnostic reference standard. Consultants’ diagnoses served as an additional reference standard. The optimal priority point cutoff score was determined using receiver operating characteristic (ROC) curve analysis.

Area under the ROC curve ranged from 0.715 (95% CI = 0.645–0.785, P < 0.001) for consultant diagnoses to 0.857 (95% CI = 0.808–0.907, P < 0.001) for modified DSM-IV-TR criteria. The latter was associated with 69.6% sensitivity and 90.7% specificity.

Agreement was best between IEC criteria with a cutoff score of 74 and modified DSM-IV-TR criteria (sensitivity 69.6%, specificity 90.7%); this cutoff score demonstrated the highest agreement in all comparisons. Consultant diagnoses showed much better agreement with modified, compared to original, DSM-IV-TR criteria, suggesting that the DSM-IV-TR criterion of “severe” rigidity may be more restrictive than what most knowledgeable clinicians use in practice.

The authors have not supplied their declaration of competing interest.