Validity of the Dutch modified painDETECT questionnaire (MPDQ-NL) for patients with hip or knee osteoarthritis

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.