Validity and reliability of the Spanish version of the DN4 (Douleur Neuropathique 4 questions) questionnaire for differential diagnosis of pain syndromes associated to a neuropathic or somatic component

Table 4 Comparison of the psychometric properties of validity for differential diagnosis of neuropathic pain vs non-neuropathic pain for a cut-off value ≥ 4 points in the Spanish version of the DN4 questionnaire, in the overall sample and in patients with pure neuropathic pain (excluding those with mixed pain) and with peripheral neuropathic pain (excluding patients with mixed and central pain).

	All patients (n = 158)	Mixed pain excluded (n = 116)	Mixed and central pain excluded (n = 84)
Youden index	0.58	0.60	0.60
Sensitivity (%)	79.8% (71%–87%)	81.7% (70%–91%)	82.1% (63%–94%)
Specificity (%)	78.0% (65%–88%)	78.0% (65%–88%)	78.0% (65%–88%)
PPV (%)	85.9% (77%–92%)	79.0% (67%–88%)	63.9% (46%–79%)
NPV (%)	69.7% (57%–80%)	80.7% (68%–90%)	90.2% (79%–97%)
AUC	0.85 (0.79–0.91) ^†	0.87 (0.80–0.93) ^†	0.87 (0.78–0.96) ^†
% of agreement	79.1% (72%–85%) ^§	79.8% (72%–87%) ^§	79.3% (69%–87%) ^§
Kappa's Agreement	0.56 (0.43–0.70) ^‡	0.60 (0.45–0.75) ^‡	0.56 (0.39–0.74) ^‡

Youden index = Sensitivity + Specificity – 1, 95% confidence interval in brackets, PPV = Positive Predictive Value, NPV = Negative Predictive Value, AUC = Area under the curve (ROC curve analysis). ^†p < 0.001 (p value in ROC curve analysis), ^§p > 0.05 between reference diagnosis and DN4 classification for a cut off value ≥ 4 pts (McNemar's test), ^‡ p < 0.001 (p value for Cohen's kappa of agreement between reference diagnosis and DN4 classification for a cut off value ≥ 4 pts).

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