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LetterCorrespondence

Drs. Dai and Felson reply

Zhaoli Dai and David T. Felson
The Journal of Rheumatology February 2021, 48 (2) 303; DOI: https://doi.org/10.3899/jrheum.201222
Zhaoli Dai
1Centre for Health Systems and Safety Research, Australian Institute of Health Innovation, Faculty of Medicine, Health and Human Sciences, Macquarie University, and The University of Sydney, Faculty of Medicine and Health, School of Pharmacy, Sydney, Australia;
2Boston University School of Medicine, Department of Medicine, Section of Rheumatology, Boston, Massachusetts, USA;
PhD
Roles: Research Fellow
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  • For correspondence: joy.dai-keller@mq.edu.au
David T. Felson
2Boston University School of Medicine, Department of Medicine, Section of Rheumatology, Boston, Massachusetts, USA;
3Centre for Epidemiology, University of Manchester and the NIHR Manchester BRC, Manchester University NHS Trust, Manchester, UK.
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To the Editor:

We appreciate the interest and comments by Yang and Hung1 in our recent publication, “Sleep Quality Is Related to Worsening Knee Pain in Those with Widespread Pain: The Multicenter Osteoarthritis Study”2. Yang and Hung raised 3 issues about potential biases in the methodology in our study around (1) the assessment methods used for sleep quality, (2) confounding factors such as other pain medication used, and (3) the appropriateness of causality in the study conclusion1.

Regarding the first point, we have recognized in our report that using a single questionnaire item for sleep quality adopted from the Pittsburgh Sleep Quality Index or restless sleep frequency drawn from the Center for Epidemiologic Studies Depression Scale in the past week to estimate sleep quality was a major limitation of the study. However, our findings have suggested that these 2 sleep measures were moderately high using Spearman correlation (r = 0.69) and that their relationships were coherent with consistent frequent knee pain and with knee pain worsening when widespread pain was present. To elaborate further, the approach of using a single item to estimate sleep quality has been shown as a valid, simple, and practical method in clinical research3. Earlier reviews have indicated that sleep variables, including sleep duration, self-reported sleep, and number of awakenings, were stable among older adults4,5. Adding data on sleep quality during the 2-year follow-up may introduce reverse causality, in which pain could affect sleep quality. These are minimized by assessing sleep quality as a predictor of later pain.

For the second point, nonsteroidal antiinflammatory drugs were the most commonly used pain drugs for knee pain in subjects in the Multicenter Osteoarthritis Study and at any rate, one would not expect that pain medication mentioned by Yang and Hung1 would alter the difference between the association of sleep and generalized but not localized pain. Hence, we believe that the pain medications mentioned by Yang and Hung would not confound the relationships assessed in our study.

For the third point raised, we would like to clarify our results. For the frequent consistent knee pain outcome, we found statistically significant results in the cross-sectional analysis for the prevalence of the condition, but not in the longitudinal analysis for the incidence of the condition. However, for knee pain worsening, in longitudinal analyses between baseline and 2 years later for change in knee pain worsening, we found statistically significant results, particularly when widespread pain was present2. These results have indicated potential causal inferences between sleep quality and knee pain worsening, depending on the status of widespread pain. Since this study is not a randomized clinical trial, no causality has been confirmed. We recognized this in our report that “future studies with longterm comprehensive and objective sleep assessments are needed to verify these results to elucidate the effect of sleep on knee pain when other body pain comorbidities exist.”2.

In summary, we hope that we have addressed Yang and Hung’s concerns on biases in the methods in our study1. These concerns have been recognized in our original report2 and are further explained in this correspondence.

  • Copyright © 2021 by the Journal of Rheumatology

REFERENCES

  1. 1.↵
    1. Yang CC,
    2. Hung PC.
    Bias in the methodology: sleep quality is related to worsening knee pain in those with widespread pain. J Rheumatol 2021;48:303.
    OpenUrlFREE Full Text
  2. 2.↵
    1. Dai Z,
    2. Neogi T,
    3. Brown C,
    4. Nevitt M,
    5. Lewis CE,
    6. Torner J, et al.
    Sleep quality is related to worsening knee pain in those with widespread pain: The multicenter osteoarthritis study. J Rheumatol 2020;47:1019-25.
    OpenUrlAbstract/FREE Full Text
  3. 3.↵
    1. Snyder E,
    2. Cai B,
    3. DeMuro C,
    4. Morrison MF,
    5. Ball W.
    A new single-item sleep quality scale: Results of psychometric evaluation in patients with chronic primary insomnia and depression. J Clin Sleep Med 2018;14:1849-57.
    OpenUrlCrossRef
  4. 4.↵
    1. Ohayon MM,
    2. Carskadon MA,
    3. Guilleminault C,
    4. Vitiello MV.
    Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: Developing normative sleep values across the human lifespan. Sleep 2004;27:1255-73.
    OpenUrlCrossRefPubMed
  5. 5.↵
    1. Li J,
    2. Vitiello MV,
    3. Gooneratne NS.
    Sleep in normal aging. Sleep Med Clin 2018;13:1-11.
    OpenUrlCrossRefPubMed
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1 Feb 2021
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The Journal of Rheumatology Feb 2021, 48 (2) 303; DOI: 10.3899/jrheum.201222
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