Why You Should Consider Central Mechanisms When Treating Endometriosis

“It is often associated with negative cognitive, behavioural, sexual or emotional consequences, as well as with symptoms suggestive of lower urinary tract, sexual, bowel or gynaecological dysfunction.”¹ Engler et al 2021 also extend this definition to comment that endometriosis may be an incidental finding, is not always painful, and the degree of disease seen laparoscopically does not correlate well with symptom severity. This is routinely seen in clinical practice, where many patients continue to experience debilitating pelvic pain, bladder, bowel or sexual dysfunction despite optimal gynaecological treatment and laparoscopic excision of the endometrial lesions. 

 

 

The presence of endometrial lesions may contribute to local inflammatory and nociceptive input. It is widely accepted that persistent pain will occur due to a multitude of other factors, beyond the endometrial lesions ^2-7 including uterine, urologic, gastrointestinal, musculoskeletal, nervous system and psychological factors⁷.  This can lead to further nervous system sensitisation, including a combination of peripheral, central and cross-organ sensitisation⁸.  

 

Whilst further study and validation is needed, Yong and co-authors (2020) proposed that EAP could be classified into four different phenotypes⁷: 

 

 

Belgian physiotherapist and pain researcher Dr Jo Nijs is a leader in the study of central pain mechanisms and their implication for clinical practice.  He states these mechanisms include changes to sensory processing in the brain, reduced functioning of the descending inhibitory pathways (the brake) and increased activity of facilitatory nociceptive pathways (the accelerator)⁹. The accelerator is further enhanced by emotions and thoughts.  The combination of increased acceleration and decreased brakes within the central nervous system leads to the picture of altered (often increased) sensitivity to multiple stimuli such as pressure, stress, light, cold, heat, chemicals, sound and electricity.  Central sensitisation is one component of central pain mechanisms, and is the most commonly used term in the literature.  Nijs describes central sensitisation as “an amplification of neural signalling within the central nervous system that elicits pain hypersensitivity⁹.”

 

Central pain mechanisms can be recognised clinically by a number of typical features, which include:

 

 

If central pain mechanisms are present, it predicts poor outcome following classical local treatments such as electrotherapy, motor control exercises and surgery.  Treatment of patients in whom central sensitisation is present should address the lifestyle factors that sustain the process of central sensitisation, including illness beliefs, stress, sleep, physical activity and diet.¹⁰

 

 

When assessing EAP, it is important to start with a thorough history to carefully consider the various contributors of both central and peripheral pain mechanisms.  Each patient presents with substantial variability of these factors.  This variability demands a biopsychosocial approach utilising a multi-disciplinary team, to address the specific phenotypes of peripheral and central factors within each patient². 

 

One tool that may be used to assess central pain mechanisms is the Central Sensitisation Inventory (CSI).  It has high reliability and validity and has recently been tested in an endometriosis population¹¹.   A score of greater than 40 in Part A indicates that central pain mechanisms are likely present. Part B lists common conditions that are associated with central sensitisation eg. irritable bowel syndrome or fibromyalgia. If a patient scores > 40 OR has one or more of the comorbid conditions in Part B, the likelihood of central pain mechanisms influencing their pain journey is greater.

 

It is important that everyone involved in supporting those who experience endometriosis think beyond the pelvis and considers central pain mechanisms. The CSI is a simple and practical tool that can be used to assist in phenotyping patients with EAP and also help to counsel patients on the presence of central factors that may be influencing their pain⁶, so that appropriate referrals can be made (eg to physiotherapy, psychology, dietician, exercise physiologist) and the appropriate lifestyle factors can be addressed as part of their treatment plan.   This is more likely to be effective at improving pain, function and quality of life for these patients².