Samenvatting

Purpose: The etiology of pain in osteoarthritis (OA) is complex and multifactorial. A growing number of studies suggest that modification of pain-transmission in the peripheral and central nervous system, leading to sensitization, plays a role in OA pain. Sensitization seems to be associated with neuropathic pain-like symptoms and assessment of these symptoms can help to identify patients who could benefit from additional treatment options. Several questionnaires are available to distinguish neuropathic from nociceptive pain symptoms. The modified painDETECT questionnaire (mPDQ) is a self-reported questionnaire developed to discriminate between nociceptive- and possible/likely neuropathic pain in knee OA patients. Recently the mPDQ was translated into Dutch and adjusted to also fit hip OA patients. The aim of this study was to assess the validity of the mPDQ-NL in patients with hip or knee OA. Methods: Primary hip and knee OA patients were recruited from three Dutch hospitals. Based on previous research, confirmatory factor analysis for two principal components was performed to assess structural validity. Construct validity (both convergent and divergent) was assessed using hypothesis testing. Predefined hypotheses were formulated concerning the correlation between the mPDQ-NL and the Self-reported Leeds Assessment of Neuropathic Symptoms and Signs (SLANSS), subscales of the Knee injury and Osteoarthritis Outcome score/ Hip disability and Osteoarthritis Outcome Score (KOOS/HOOS), Visual Analogue Scale for pain (VAS pain), and subscales of the RAND-36 health survey (RAND-36). According to the COSMIN criteria, construct validity of a questionnaire is sufficient if 75% of predefined hypotheses are met. Additionally, convergent validity was assessed with blunt Pain Pressure Thresholds (PPTs) in a subsample of participants. A reduced PPT is a somatosensory abnormality that is considered an indication of sensitization in OA. Therefore it was expected that reduction of PPTs was associated with higher mPDQ scores. Results: 168 participants were included. PPT measurements were performed in a sample of 46 participants. Factor analysis confirmed two principal components. The items that loaded on the first component could be described as “evoked neuropathic sensations”, the items that loaded on the second component as “spontaneous neuropathic sensations”. However there were two items that substantially loaded on both components. The item regarding pain pattern did not load on any component. Considering construct analysis, 80% of the predefined hypotheses concerning the correlation between mPDQ and self-reported questionnaires were met. Considering the correlation with PPT measurements, 50% of the predefined hypotheses were met. Conclusions: The mPDQ-NL seems to adequately reflect neuropathic pain-like symptoms experienced by hip and knee OA patients. Concerning structural validity, two determinative components seem to be present, in line with previous research. However, one particular item regarding pain pattern might not reflect the construct of neuropathic pain-like symptoms in hip or knee OA. Therefore, when using the mPDQ in hip or knee OA patients, it might be considered to skip this particular item. Construct validity can be considered sufficient, with over 75% of the predefined hypotheses regarding correlation between the mPDQNL and other questionnaires were met. However, only 50% of the hypotheses concerning PPT measurements were met, probably due to heterogeneity and limited sample size of this subgroup. To our knowledge, this study is the first to assess the structural validity of the mPDQ knee and hip by using factor analysis and to assess construct validity using elaborate hypothesis testing as proposed by the COSMIN guidelines.