Understanding the baseline

Each individual patient and population of patients have baseline characteristics, and an understanding of the multidimensional nature of the patient can help identify appropriate expectations and define treatment success. A 2020 publication by our group reported the baseline multidimensional characteristics of a broad sample of patients (n = 19,546) presenting to a chronic pain clinic using the Patient Reported Outcomes Measurement Information System (PROMIS) 29-question battery. This aimed at defining the population distribution of those subdomains, notably indicating a baseline level in this population of 0.5–1.4 standard deviations above the US general population.

Discussing the baseline with the patient in the context of any intervention is critical to determining treatment success for that individual. This also allows the clinician to devise a multimodal strategy to improve patient quality of life by addressing biopsychosocial contributors to pain.

Minimum clinically important difference (MCID)

Meaningful change is ultimately the defining estimate of treatment effectiveness from a clinical perspective. The minimum clinically important difference (MCID) is not a static value for any outcome measure, but is a range that depends on the methods used. In other words, each outcomes measure and each change in any outcomes measure must be contextually interpreted to be meaningful to the patient. The primary methods for determining MCID are (1) anchor-based and (2) distribution-based.

• 1.
  

  Anchor-based methods reflect the perspective ‘anchored’ around a specific event or episode of care. For example, “since the [anatomic area] ablation procedure, how would you describe your [anatomic area(s)] pain now?” [visual analogue scale]

  
  
• 2.
  

  Distribution-based methods reflect the variability in scores across a large population and use that to discern normal fluctuations from true change.

Anchor-based methods are typically the most relevant in the context of pain care procedures, and the anchor parameters may be narrowed or broadened as needed to understand the patient impact. Distribution-based methods are helpful to contextualize individual treatment and research across the population. The MCID value selected may be different depending on the intended use of the instrument, from lower MCID for conservative care and higher MCID values for higher risk/reward care and outcomes.

The patient value judgement does not always equal the MCID, and as clinicians it is our goal to ensure that the patient response is appropriately and individually captured. Corroborating various PROs with physical examination and other data points such as medication changes or activity changes must be done to ensure adequate capture of treatment success.

Universal outcomes measures

In general, a universal outcomes battery will describe quality of life and include a variety of relevant subdomains related to pain and the pain experience. This is also termed Health-related Quality of Life (HrQOL).

PROMIS-29 is a universally relevant outcomes battery that reports pain intensity, pain interference, physical function, sleep disturbance, fatigue, depression, anxiety, and social participation. An online resource supported by the NIH is available that provides validated equivalent scores for different health outcomes measures in terms of current PROMIS measures (PROSetta Stone®, http://www.prosettastone.org ).

EuroQol 5-Dimensional (EQ5D) was developed in 1990 and refined in 2011 and is generalizable to the European population. Work has been done to create cross-talk and estimate EQ5D scores using PROMIS elements, allowing for forwards and backwards compatibility in the future. ^,

Pain-specific outcomes measures

The Neck Disability Index contains 10 items related to the neck and is a long-used battery to estimate disability due to a painful condition. This is the most widely used PRO for neck disorders, but the psychometric properties of the test (i.e., does it assess what it intends to assess?) have been questioned and contribute to inconsistency in MCID from 5 to 10 points across studies.

Oswestry Disability Index is a 10-item questionnaire that evaluates disability and pain related to the low back and has long been used as a primary endpoint in spine surgery. ^,

PROMIS Pain Interference (PI) and Physical Function (PF) have been shown to be responsive in a variety of pain and spine conditions and represent a question burden reduction as compared to legacy measures.

Outcomes for diagnostic procedures

Pain is complex, and it is oftentimes challenging to identify a particular pain generator or group of overlapping pain generators based on physical examination and other diagnostics alone. The term ‘diagnostic procedure’ is used in this context to refer to any injection intended to either confirm or support a diagnosis, and/or to select patients for a definitive therapy (i.e., radiofrequency ablation, device implantation, etc.).

Outcomes for diagnostic procedures are typically assessed in an anchor-based approach, such as by using a pain diary to record percent pain relief (0 = no relief, 100% = complete relief), numerical pain scores, and/or functional achievements. The time course for these outcomes are short, on the order of hours due to the duration of action of local anesthetics.

Outcomes for therapeutic procedures

The timing for assessment of outcomes with respect to therapeutic procedures varies in terms of domain assessed. Adverse events or other negative outcomes are typically encountered in the days after these procedures, such as neuritis after radiofrequency ablation or postdural puncture headache. Alternatively, the clinically meaningful benefit of these procedures must be durable in order for it to be sustainable, such that the outcomes for therapeutic procedures must be reported longitudinally using responsive measures.

Figure 19.1 provides a contextual algorithm for building an outcomes campaign in addition to capturing an essential data set to understand the patient journey holistically.

For most radiofrequency ablation therapies, the appropriate timeframe for follow-up should be divided into surveillance for complications (0 to 4 weeks), followed by assessment of effect (1 to 24 months).