What is the difference between the Palliative Performance Scale (PPS) and the Karnofsky score?

Differences Between Palliative Performance Scale (PPS) and Karnofsky Performance Score

The Palliative Performance Scale (PPS) is a modified version of the Karnofsky Performance Status (KPS) scale specifically designed for use in palliative care settings, with key differences in their structure, application, and scoring parameters. Both scales measure functional status but the PPS is specifically tailored for palliative care patients with additional parameters beyond physical function, while the Karnofsky scale is more broadly used in oncology to determine treatment eligibility.

Scale Origins and Development

• Karnofsky Performance Status (KPS):

  • Developed earlier as a general measure of patient activity and medical care requirements in cancer patients 1
  • Considered the gold standard for quantifying physical functioning of cancer patients 2
  • Uses an 11-point scale from 0-100% in 10% increments 3

• Palliative Performance Scale (PPS):

  • Introduced in 1996 as a modification of the KPS specifically for palliative care 4
  • Designed to address limitations of KPS in the hospice/palliative setting 2
  • Uses a similar 0-100% scale in 10% increments but with different descriptors 5

Key Structural Differences

1. Assessment Parameters:

   • KPS: Primarily focuses on physical function and independence 1
   • PPS: Incorporates five domains: ambulation, activity level/evidence of disease, self-care, oral intake, and level of consciousness 5

2. Reference to Location of Care:

   • KPS: Contains references to hospitalization and institutional care 2
   • PPS: Avoids reference to location of care, making it more applicable across settings 2

3. Bed Time Assessment:

   • KPS: Less specific about proportion of time spent in bed
   • PPS: Includes specific descriptors for the proportion of time spent in bed 2

Clinical Application Differences

1. Primary Use Context:

   • KPS: Widely used in oncology clinical trials and treatment decision-making 6
   • PPS: Primarily used in palliative care for communication, workload analysis, and potentially prognostication 4

2. Treatment Decision Thresholds:

   • KPS: Critical threshold at KPS ≥60% for systemic therapy eligibility 7
   • PPS: Used more for care planning and resource allocation in palliative settings 5

3. Correlation with Survival:

   • KPS: Strong correlation with overall survival and progression-free survival in cancer treatment 7
   • PPS: Demonstrated correlation with survival time in hospice settings (e.g., PPS 10%: 1.88 days; PPS 50%: 13.87 days) 4

Scale Equivalence

• ECOG PS 0-1 ≈ KPS 80-100%
• ECOG PS 2 ≈ KPS 60-70%
• ECOG PS 3-4 ≈ KPS <60% 7

Reliability and Validity

• Both scales have demonstrated good reliability in formal studies:
  • KPS: Interrater reliability of 0.97 in trained observers 3
  • PPS: Intraclass correlation coefficients >0.93 across multiple testing scenarios 5

Clinical Implications

• The PPS may be more sensitive and objective for home hospice patients, with scores typically lower and spread over a wider range than KPS scores for the same patients 2
• KPS is more commonly used in determining eligibility for clinical trials and systemic therapy 6
• PPS provides more specific information relevant to palliative care planning and resource allocation 5

Potential Pitfalls

• Both scales are subject to some subjectivity in assessment
• KPS may overestimate functional status in home settings compared to clinic evaluations 1
• Age bias exists in performance status assessment, with clinicians tending to assign higher (worse) scores to older patients despite similar objective physical activity levels 7

When choosing between these scales, consider the primary purpose of assessment and the care setting, with PPS generally being more appropriate for patients in palliative care programs.