Nociplastic Pain in Patients Diagnosed With Subacromial Pain Syndrome (SAPS)

Identification of the Prevalence of Nociplastic Pain Phenotype in Patients Diagnosed With Subacromial Pain Syndrome (SAPS) - a Cross-sectional Study

The goal of this cross-sectional study is to estimate the prevalence of nociplastic pain phenotype, according to the IASP clinical criteria, among patients diagnosed with SubAcromial Pain Syndrome (SAPS).

The main question it aims to answer is: Prevalence of nociplastic pain phenotype in patients diagnosed with SAPS in an outpatient clinic.

Primary outcome: Proportion of patients with SAPS meeting the IASP criteria for nociplastic pain.

Musculoskeletal pain poses a significant burden on both individuals and the society. The International Association for the Study of Pain (IASP) describes different pain mechanisms including nociceptive, neuropathic and nociplastic pain. Identification of different pain mechanisms may be relevant for understanding pain presentation and treatment response in patients with musculoskeletal pain.

Shoulder pain ranks among the most prevalent musculoskeletal complaints with subacromial pain syndrome (SAPS) diagnosis being the most prevalent and serves as a common diagnose for non-traumatic shoulder pain. Exercise and other conservative treatments are considered first line treatment modalities in SAPS. However, a substantial proportion of patients experience limited or transient treatment effects and may develop chronic shoulder pain. This modest effect may be explained by a potential mismatch between the pain phenotype and the mechanistic assumption behind the treatment.

There are emerging clinical consensus statements to identify primary pain phenotypes in musculoskeletal pain conditions. The IASP criteria for nociplastic pain offer a structured approach for classifying patients based on clinical features. However, the IASP criteria for identifying nociplastic pain have not, to our knowledge, been sufficiently investigated among patients with SAPS to elucidate the distribution of pain phenotypes among this population of shoulder patients.

Movement-evoked pain is a key feature in many patients with SAPS. Virtual Reality (VR) may provide a controlled enviroment in which visual feedback and percevied movement can be manipulated. Such manipulation may influence movement-evoked pain and could potentially provide additional information about pain responses associated with different pain phenotype. In this study, VR is therefore included as an exploratory assessment.

The primary aim of this cross-sectional study is to investigate the proportion and characteristics of patients diagnosed with SAPS who meet the IASP clinical criteria for nociplastic pain in an outpatient hospital setting.

The Primary objective is to estimate the prevalence of nociplastic pain phenotype, according to the IASP classification, among patients with SAPS.

The exploratory objective is to investigate the relationship between movement- evoked pain responses during manipulated VR conditions and pain phenotype.

The exploratory hypothesis is that patients classified as having a nociplastic pain phenotype will demonstrate greater changes in pain intensity and movement-evoked pain responses during the VR conditions, compared with patients not classified as having a nociplastic pain phenotype.

Inclusion Criteria:

1. Diagnosed with SAPS (dm751, dm753, dm754, dm755
2. Shoulder pain ≥ 3 months
3. ≥ 3 out of 5 specific shoulder test
4. Age 18-70 years
5. Increased pain during active arm elevation
6. Pain during active elevation ≥ 3 (VAS)

Exclusion Criteria:

1. Severe impaired vision
2. Epilepsies
3. Severe cognitive or physical impairment
4. Language barrier (danish)