Abstract Introduction Hard Flaccid Syndrome (HFS) involves episodic hyperactivity of the hypogastric nerve to the penis, scrotum, pelvic floor muscles/pelvis. HFS patients in a symptomatic flare often complain of an uncomfortable flaccid penile shaft that is shrunken, turtle-like and firm, with the glans penis pale-looking and cold. Forward-looking infrared (FLIR) is a non-invasive, portable, user-friendly thermal imaging technology that provides real-time, non-contact detailed thermal images of skin temperature. Objective This study is an initial evaluation of use of FLIR for diagnosing and monitoring HFS patients by objectively measuring temperature of the flaccid and erect penile glans and shaft skin surfaces. Methods We identified patients who presented to our clinic between July 21, 2025 and October 17, 2025 for management of their HFS or other sexual dysfunctions. Evaluation consisted of completion of patient reported outcome measures, psychologic assessment, history and physical examination, quantitative sensory testing, and grayscale and Doppler ultrasound during pharmacologic erection. FLIR (E86-EST) thermography was performed in both flaccid and erect states with the patient lying supine with automatic correction for differences in room temperature. The penis was positioned to face upward and outward in the midline. Thermal photographs of the penis, mid-shaft and glans were taken and skin temperatures in the flaccid and erect state were recorded. Data were analyzed by unpaired t-test using Welch’s correction and one-way ANOVA followed by post-hoc pairwise comparisons using Tukey’s test. Results A total of 250 thermal images from 12 HFS patients (aged 36.4±11.1 yrs) and 38 no HFS patients with other sexual dysfunctions (aged 49.4±16.8 yrs) were included. Mean temperatures of the flaccid glans, flaccid mid-shaft, erect glans and erect mid-shaft in HFS patients were 88.2°, 94.0°, 93.5°, and 94.9° F, respectively. Those temperature values in no HFS patients were 91.4°, 94.6°, 94.6°, and 95.7° F, respectively. For both groups, the flaccid glans temperature was significantly lower (p0.001) than the flaccid mid-shaft, erect glans and erect mid-shaft. The flaccid glans in the HFS group was significantly lower (p=0.0003) than the flaccid glans in the no HFS group (Figure 1). In 5 patients who achieved relief of HFS symptoms from various treatments their mean flaccid glans temperature increased from 86.6 (Figure 2a) to 89.9°F (Figure 2b), similar to the no HFS group. Conclusions HFS is a bothersome sexual dysfunction with physiologic changes to the penis. To better manage HFS, objective measures such as FLIR may be utilized. Using the information gleaned from this research, several patients who had previously not revealed they had HFS symptoms have been diagnosed, thus showing the benefit of FLIR for both diagnosis and assessment of treatment. Disclosure No
Koontz et al. (Mon,) studied this question.