Quantitative Sensory Testing in Endometriosis Patients With Cyclic vs. Non-Cyclic Pain-A Case-Control Study

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Endometriosis patients displayed significant cold and pressure hyperalgesia, suggesting peripheral sensitization is the primary mechanism underlying their pain.

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This case-control study used standardized quantitative sensory testing (QST) in women with endometriosis to compare somatosensory profiles versus healthy controls and to contrast patients with cyclic versus non-cyclic pain, aiming to identify peripheral or central sensitization patterns. Endometriosis patients showed significant hyperalgesia to cold and blunt pressure in the affected body area, with the non-cyclic subgroup more affected than the cyclic subgroup, and the dominant finding was pronounced pressure hyperalgesia that was regionally restricted and present in every patient; higher thermal and tactile detection thresholds also suggested somatosensory loss, while pinprick hyperalgesia and facilitated pain summation were not significantly increased. The paper explicitly interprets the overall QST pattern as more consistent with peripheral than central sensitization, noting findings were mainly limited to certain QST modalities rather than a broad central sensitization signature. This paper is centrally about endometriosis — it uses QST to characterize somatosensory alterations distinguishing cyclic from non-cyclic endometriosis pain.

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Abstract

BACKGROUND: Endometriosis is a chronic, inflammatory disease with considerable symptom load in affected female patients. Cyclic pain (associated with menstruation) dominates in most patients, but few patients suffer from persistent non-cyclic pain. This study aims to investigate whether the somatosensory profile in endometriosis differs from healthy controls or between cyclic and non-cyclic subtypes. Moreover, we aimed at potential identifiers of peripheral or central nervous sensitization underpinnings of endometriosis in the QST profile. METHODS: The standardised investigation protocol for quantitative sensory testing (QST) of the German research network of neuropathic pain was used to find possible differences compared to healthy controls or between cyclic and non-cyclic subtypes of endometriosis potentially providing hints for altered peripheral and central nociceptive processing. RESULTS: Endometriosis patients showed significant hyperalgesia to cold and blunt pressure in the affected body area (non-cyclic>cyclic, all p  0.30). Exaggerated pressure hyperalgesia was most pronounced, regionally restricted and present in every patient (p << 0.0001). Higher thermal and tactile detection thresholds indicated non-nociceptive somatosensory loss, which differed only marginally between subgroups. Thermal loss and hyperalgesia to cold, heat and blunt pressure were also identified to a lesser extent in a remote test site (hand dorsum). CONCLUSIONS: Endometriosis patients exhibited a pattern of somatosensory changes that is consistent with peripheral rather than central sensitization. Primary afferent sensitization facilitating spinal transmission of convergent input from the affected and suprapubic referred pain area is the most likely mechanism of hyperalgesia in endometriosis. SIGNIFICANCE STATEMENT: Pain and hyperalgesia are amongst the most burdensome features in endometriosis. This QST case-control study in endometriosis patients identifies massive pressure hyperalgesia as the most significant somatosensory alteration in the viscerotome of the lower abdomen, which is easily accessible for testing in patients. This finding highlights the role of peripheral sensitization as the dominant mechanism of endometriosis-related hyperalgesia, which has major implications for future treatment, which may target prevention of peripheral sensitization by suppression of NGF or TRPV1 receptors.
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Abstract

Background Endometriosis is a chronic, inflammatory disease with considerable symptom load in affected female patients. Cyclic pain (associated with menstruation) dominates in most patients, but few patients suffer from persistent non-cyclic pain. This study aims to investigate whether the somatosensory profile in endometriosis differs from healthy controls or between cyclic and non-cyclic subtypes. Moreover, we aimed at potential identifiers of peripheral or central nervous sensitization underpinnings of endometriosis in the QST profile.

Methods

The standardised investigation protocol for quantitative sensory testing (QST) of the German research network of neuropathic pain was used to find possible differences compared to healthy controls or between cyclic and non-cyclic subtypes of endometriosis potentially providing hints for altered peripheral and central nociceptive processing.

Results

Endometriosis patients showed significant hyperalgesia to cold and blunt pressure in the affected body area (non-cyclic>cyclic, all p 0.30). Exaggerated pressure hyperalgesia was most pronounced, regionally restricted and present in every patient (p << 0.0001). Higher thermal and tactile detection thresholds indicated non-nociceptive somatosensory loss, which differed only marginally between subgroups. Thermal loss and hyperalgesia to cold, heat and blunt pressure were also identified to a lesser extent in a remote test site (hand dorsum).

Conclusions

Endometriosis patients exhibited a pattern of somatosensory changes that is consistent with peripheral rather than central sensitization. Primary afferent sensitization facilitating spinal transmission of convergent input from the affected and suprapubic referred pain area is the most likely mechanism of hyperalgesia in endometriosis. Significance Statement Pain and hyperalgesia are amongst the most burdensome features in endometriosis. This QST case–control study in endometriosis patients identifies massive pressure hyperalgesia as the most significant somatosensory alteration in the viscerotome of the lower abdomen, which is easily accessible for testing in patients. This finding highlights the role of peripheral sensitization as the dominant mechanism of endometriosis-related hyperalgesia, which has major implications for future treatment, which may target prevention of peripheral sensitization by suppression of NGF or TRPV1 receptors. Conflicts of Interest The authors declare no conflicts of interest. Supporting Information | Filename | Description | |---|---| | ejp70163-sup-0001-Supinfo01.jpgJPEG image, 75.5 KB | Data S1: ejp70163-sup-0001-Supinfo01.jpg. | Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis

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