Chronic pain in rheumatology

Rheumatology is the internal medicine specialty that studies and treats diseases of the musculoskeletal system. Although the pathophysiological mechanisms may differ from one disease to another, pain is the most frequent symptom and the main reason patients seek medical help.

In rheumatology, chronic pain predominates. It is defined as pain that persists beyond the time required for tissue healing. The International Association for the Study of Pain (IASP) defines chronic pain as that which persists or recurs for more than three months.

In the classification of chronic pain proposed by the IASP task force for the ICD-11, rheumatic diseases may fall under primary chronic pain (e.g., fibromyalgia), musculoskeletal pain, or neuropathic pain.

Challenges in pain measurement

Pain is a multidimensional symptom, particularly when chronic, as it involves the original lesion or "trigger," associated symptoms such as fatigue, sleep, and cognitive disturbances, and impacts on personal, family, and social life.

Treating patients with chronic pain, regardless of the underlying disease, involves challenges inherent to its multidimensional nature. One major challenge is how to measure the outcomes of interventions. Is it possible to measure pain? Research has explored various instruments, but they have seen limited use in daily clinical practice.

Unidimensional scales

The most common tools are analog scales, considered unidimensional since they measure only intensity without considering other clinical aspects. These scales can take several forms, such as visual (100 mm line), numerical (0 to 10 or 0 to 100), facial expressions, and colors. The choice depends on patient characteristics, such as age and cognitive function. Gallasch & Alexandre compared four types of these scales in low-education populations and found that numerical scales were most appropriate, with an intraclass correlation coefficient of 0.99. The ease and short time required make these the most widely used tools. However, it is known that pain has impacts beyond intensity alone. In practice, low-intensity pain can be just as disruptive as more severe pain. Other aspects, such as functionality and degree of suffering, are also important. Unidimensional scales fail to capture this complexity.

Multidimensional instruments

In contrast, multidimensional questionnaires can assess not only pain intensity but also other associated phenomena, disability level, emotional state, and social and occupational impacts.

Multidimensional questionnaires may be specific to chronic pain or more general tools assessing quality of life and overall health status. There are also questionnaires designed for specific diseases or syndromes such as fibromyalgia, chronic low back pain, migraine, and temporomandibular dysfunction. Complementary tools exist to evaluate depression, anxiety, fatigue, and sleep.

Among the multidimensional tools for pain assessment, the Brief Pain Inventory (BPI) and the McGill Pain Questionnaire (MPQ) stand out. The BPI uses a 0 to 10 scale to assess pain intensity and its interference with walking, daily activities, work, social activities, mood, and sleep. The MPQ comprises 78 descriptors across four groups and 20 subcategories: sensory-discriminative, affective-motivational, evaluative-cognitive, and miscellaneous. Each subcategory has 2 to 6 descriptors. The MPQ also includes a pain intensity rating item and has a shorter version (Short Form).

Other multidimensional tools include the Clinically Aligned Pain Assessment (CAPA) Tool, Defense and Veterans Pain Rating Scale, Geriatric Pain Measure, Pain Impact Questionnaire (PIQ-6), Pain Monitor, and the SF-36 Bodily Pain Scale.

Specific tools for syndromes

Specific questionnaires include the Revised Fibromyalgia Impact Questionnaire (FIQR), the Fibromyalgia Scale (FS), and the Central Sensitization Inventory (CSI).

The FIQR, created in 1991 and revised in 2009, addresses daily activities, professional activities, and symptom intensity. Scores range from 0 to 100, where 0 indicates no impact and 100 the maximum possible impact.

The FS, also known as the Polysymptomatic Distress Scale (PDS), sums the two indices used in the preliminary criteria for fibromyalgia diagnosis (ACR 2010/2011/2016): the Widespread Pain Index and the Symptom Severity Score. It ranges from 0 to 31 and suggests fibromyalgia exists on a continuum rather than as a categorical condition.

Assessment of nociplastic pain in rheumatic diseases can be conducted using the Central Sensitization Inventory. Part A includes 25 statements rated on a 5-point Likert scale, with total scores ranging from 0 to 100. Part B asks whether the patient has previously been diagnosed with any central sensitization syndrome.

Chronic pain patient follow-up, whether in research or clinical practice, may use general questionnaires to assess health-related quality of life. Two widely used tools are the SF-36 and the WHOQOL-100. The SF-36 includes 8 scales (physical functioning, role limitations due to physical health, vitality, pain, general health perceptions, social functioning, role limitations due to emotional problems, and mental health), scored from 0 to 100 (0 = worst, 100 = best).

The WHOQOL-100 consists of 100 questions across six domains: physical, psychological, level of independence, social relationships, environment, and spirituality/religion/personal beliefs, all using a 5-point Likert scale with scores ranging from 0 to 100.

Other general tools found in the literature include the Quality of Life Scale (QoL), Health Assessment Questionnaire (HAQ), Nottingham Health Profile (NHP), EuroQol, and the Quality of Well-being Scale (QWB). Their length and complexity can hinder routine use.

Psychometric considerations and applicability

Regardless of whether scales are used for multidimensional pain assessment or specific to a condition or quality of life, one common challenge is applicability. These tools often require more time to administer and may demand detailed explanations for patients. In public healthcare settings where consultation time is limited, implementing these scales is difficult. Where other healthcare professionals are available to assist, their use may become feasible—although this is not the reality for most rheumatologists.

Another limitation is that these tools require a minimum cognitive level from patients to understand the questions. In countries with limited educational access, this poses an additional barrier.

Symptoms and comorbidities commonly associated with chronic pain also have their own metrics. Their evaluation should be considered, especially when they significantly affect individual patients or overshadow pain. In such cases, addressing these features may be a priority.

Among symptoms frequently accompanying chronic pain, fatigue is notable. For some patients, fatigue is the symptom with the greatest impact on quality of life. Thus, quantifying fatigue is important in clinical management. Tools include the Fatigue Severity Scale, Fatigue Questionnaire, Multidimensional Fatigue Inventory, Fatigue Impact Scale, and Brief Fatigue Inventory.

Sleep assessment tools include the Pittsburgh Sleep Quality Index (PSQI), Athens Insomnia Scale (AIS), Insomnia Severity Index (ISI), Mini-Sleep Questionnaire (MSQ), Jenkins Sleep Scale (JSS), Leeds Sleep Evaluation Questionnaire (LSEQ), SLEEP-50 Questionnaire, and the Epworth Sleepiness Scale (ESS).

The association between depression, anxiety, and pain is well-established. Depression assessment tools include the Patient Health Questionnaire-9 (PHQ-9), Hamilton Rating Scale for Depression (HAM-D), Beck Depression Inventory, and Zung Self-Rating Depression Scale. Anxiety tools include the Generalized Anxiety Disorder 7-item scale (GAD-7), Hamilton Anxiety Scale, and Beck Anxiety Inventory, among others.

Another emotional aspect often linked to nociplastic pain syndromes is catastrophizing. This can be measured with tools like the Pain Catastrophizing Scale.

Finally, all these tools must undergo quality validation during development. They should demonstrate content validity, internal consistency, reproducibility, and responsiveness. Additionally, cross-cultural adaptation and standardized translation are essential for use in different countries.