Responsiveness and minimal clinically important change of the Pain Disability Index in patients with chronic back pain

Spine (Phila Pa 1976). 2012 Apr 15;37(8):711-5.

Title:

Responsiveness and minimal clinically important change of the Pain Disability Index in patients with chronic back pain

Authors

Soer R

Reneman MF

Vroomen PC

Stegeman P

Coppes MH.

Study Design

Prospective cohort study

Objective

To test the responsiveness and minimal clinically important change (MCIC) of the Pain Disability Index (PDI) in patients with chronic back pain (CBP).

Summary of Background Data

1. Treatment of patients with CBP is primarily focused on reduction of disability.

2. For disability measurement, the PDI is a widely used questionnaire.

3. There are, however, no data available on responsiveness and MCIC.

Methods

1. Subjects: 242 CBP patients

2. PDI at baseline and at discharge

*2 subscales: 1 measuring voluntary activities and 1 measuring obligatory activities.

3. PDI was anchored at 2 self-reported global perceived effect (GPE) scales for complaints and self-care, respectively.

4. Responsiveness was considered sufficient when Area Under the Receiver Operating Characteristics (ROC) Curve (AUC) was higher than 0.70.

5. To test interpretability, change scores and MCIC were calculated.

6. MCIC was tested by determination of optimal cut-off point of the ROC curve and determination of specificity and sensitivity of the optimal cut-off point.

*** Pain Disability Index***

0: No disability

10: Maximum disability

Measurements

 1) Voluntary activities (PDI items 1-5)

           -family/home responsibilities, recreation, social activity, occupation, sexual behavior

 2) Obligatory activities (PDI items 6 and 7)

           -Self-care and life support activity

*** Global Perceived Effect (GPE) Scale***

GEPs were compared with PDI outcome.

2 scales reflect patient perception of disability, consisted of 7-point Likert scale (1-7)

   1: extremely worsened

   2: much worsened

   3: little worsened

   4: unchanged

   5: little improved

   6: much improved

   7: completely improved

Results

1. AUC: 0.76 and 0.77 depending on the external criterion.

2. Subscale obligatory activities did not meet the criteria for responsiveness (AUC: 0.63-0.69).

3. MCIC of the PDI was 9.5 points for GPE "complaints" and 8.5 for GPE "self-care."

Conclusion

1. Total score of the PDI as well as the subscale of voluntary activities is responsive.

2. Partly because of floor effects, the subscale obligatory activities are not sufficiently responsive.

3. However, the responsiveness of this subscale in other patient groups should be further tested.

4. In CBP patients, change can be considered clinically important when PDI score decreasing 8.5 à 9.5.

Key points

1. PDI is responsive for change with areas under the ROC curve of 0.76 and 0.77.

2. A change of 8.5 to 9.5 points on the PDI is a clinically important change in CBP patients.

4. The subscale “obligatory activities” of the PDI was found not responsive for reported complaints and self-care in patients with CBP.

"This comes from Spine (c) 2012 Lippincott Williams & Wilkins, Inc."