QST gives information about sensory healing in Gender Affirming Mastectomy

Gender Affirming Mastectomy is one of the most commonly sought-after surgical procedures in treatment of individuals with gender dysphoria which has been performed since the early 1990ies.

What is Gender Affirmation Mastectomy?

This surgery is performed in patients transitioning from female to either male or non-binary. In this type of surgery, breast tissue is removed, nipples are re-shaped or repositioned, and incisions are sought to have as little scar tissue formation, with emphasis to accentuate the pectoral muscular outline. A no-less-important factor in these surgeries is striving to minimize (persistent) post-operative pain and preserve as much sensory function as possible. However, in the most-used surgical technique for this purpose, the double incision technique, the risk of affecting sensation is highest due to the transection of the intercostal nerves that travel through the breast tissue and provide sensation to the Nipple Areola Complex (NAC).

In a 2024 publication from a group out of the Division of Plastic and Reconstructive Surgery of Weill Cornell Medicine - New York and Mass General - Boston, nerve preservation efforts using targeted NAC Reinnervation (TNR) were used in Gender Affirming Mastectomy (Remy, 2024). In TNR, the cutaneous branches of the 3rd and 5th intercostal nerves and their blood supply are preserved at a length to reach the NAC. If no sufficient length can be preserved, an acellular Avance nerve allograft is used.

What is the role of QST in surgery?

In order to assess skin reinnervation QST was used. QST is an ideal tool for testing sensory loss and preservation under different pre- and post-operative conditions as it is not invasive, gives direct and sensitive results, and as opposed to skin biopsy or electro-neurophysiology, can be easily performed by non-specialists. It can give information regarding large somatosensory nerve fibers, using vibration and mechanical stimuli like Von Frey monofilaments, as well as the smallest sensory nerve fibers, using cold and warm stimuli.

In the past, pre- and postoperative QST has been used among others to identify the best skin graft technique (Wang, 2018) in radial forearm flap surgery, and in the evaluation of neuropathy after breast cancer surgery (Mustonen, 2020) or pain after thoracotomy (Gandhi, 2020).

In this specific study, the Deutscher Forsuchsverband Neuropatischer Schmerz (DFNS) protocol was used, with Medoc’s TSA2 with 16*16 mm thermode for thermal stimuli and AlgoMed for pressure pain stimuli. QST was performed on the NAC itself and the skin of the surrounding chest in predefined quadrants.

All QST was conducted pre operatively and 12-months post-operatively, except for mechanical detection thresholds which was tested pre-operatively at 1, 3, 6, 9, 12 months post-operative.

Gender Affirming Cohort

In total 120 patients were recruited. Of them, 50 patients in total fulfilled the study, 25 who underwent the surgery with TNR, compared to age, BMI and mastectomy weight matched control patients who underwent mastectomy without TNR.

Sensory results of the surgery

For mechanical detection thresholds, pre-operative detection values were perceived at the NAC 6 months post operatively and 3 months post-operatively at the chest for the TNR patients, though not for the control patients, they reached pre-operative values for the chest at 9 months post operatively, while for the NAC preoperative values were not reached within the 12-months follow up of this study.

For cold detection thresholds there was also a statistically significant difference between TNR patients and controls in cold sensation at the NAC post-operatively (23.1°C vs. 12°C, p<0.001), while for the TNR patients these values were comparable to pre-operative values (24.6°C). Also at the chest, TNR patients had better sensory values than controls (23.6°C vs. 19.7°C, p<0.001), which were comparable to pre-operative values (23.8°C).

For warm detection there were similar results, with better warm detection at the NAC for the TNR group than for the controls (39.9°C vs. 45.8°C, p<0.001), and was comparable to preoperative values (38.4°C, p=0.2). At the chest, again, the results for the TNR group were better postoperatively compared to the controls (39.4 vs. 42.9, p<0.001), and were comparable to preoperative values (38.8°C, p=0.32).

Similarly for heat pain the results of patients who underwent TNR were better than for the controls, with 56% of patients in the control group who were able to detect heat pain before the 50°C cutoff value, compared to 100% in the TNR group. Even though heat pain thresholds in the TNR group were better than for the controls, their mean heat pain values did not reach preoperative baseline values.

In pressure pain thresholds the results were alike with more sensitivity to pressure both at the NAC and at the chest for the TNR group compared to controls, and approximate return to preoperative values for this group 12 months postoperatively.

In general, better post-operative sensitivity values were obtained from the TNR group throughout including 2-point discrimination, pinprick, and vibratory values.

Importance of sensory findings

These sensory findings all point to the advantages of the TNR technique which seems to largely preserve sensory nerve function in the long run. From the results we can conclude that large somatosensory function seemed to recover relatively fast (as measured by monofilaments), while small fiber function measured by thermal stimuli had a slower and sometimes (in heat pain) incomplete recovery 1 year post-op. Sensory function has its implications both on Quality of Life and body integration after surgery, but also plays an important role in vital and protective functions, like avoiding burns from inappropriate temperatures in the shower of from hot-packs. The patient-reported outcome measures (PROMs) in this study also pointed to better sensation as well as better nipple erection and erogenous sensation at the NAC. These measures have been linked in the past to sexual well-being, which can contribute to quality to life of these patients.

It appears that in this study again, the role of QST has been shown to be assisting in the appraisal of a surgical technique and surgical outcome. The feasibility of using thermal and pressure QST on such small areas like the nipple and the chest, have also been established in this particular study.