Erectile dysfunction (ED) is a prevalent condition affecting approximately 150 million men worldwide and is often associated with endothelial dysfunction and impaired microvascular circulation. According to the arterial size hypothesis, smaller arteries are more susceptible to early vascular impairment. Given that penile arteries (1–2 mm in diameter) show dysfunction earlier than larger arteries, we hypothesized that even smaller vessels, such as nailfold capillaries (5–10 µm in diameter), may exhibit abnormalities preceding ED onset. This study investigated whether morphological changes in nailfold capillaries, particularly increased crossing capillaries, could serve as a novel visual marker of early microvascular damage in patients with ED.

A cross-sectional study was conducted on 36 men with ED and 36 age-matched healthy controls recruited at Hitachi Medical Center from April 2022 to March 2024. Nailfold capillaroscopy was performed using a GOKO Bscan-ZD microscope at ×390 magnification. Capillary morphology was classified according to the European League Against Rheumatism (EULAR) criteria, focusing on crossing capillaries, defined as those where the limbs cross once or twice with a convex capillary head. The percentage of crossing capillaries was calculated, and participants were stratified into tertiles, with the highest tertile (≥63.9%) categorized as having a high percentage of crossing capillaries. The association between ED and a high percentage of crossing capillaries was analyzed using multivariable logistic regression, adjusting for potential confounders.

ED patients exhibited significantly higher rates of diabetes (38.9% vs. 0%) and dyslipidemia (50% vs. 8.3%) than controls. The median number of nailfold capillaries assessed per patient was 95 (interquartile range: 73–115), with a median crossing capillary percentage of 60.3% (53.9–69.5%). A high percentage of crossing capillaries (≥63.9%) was observed more frequently in patients with ED than in controls. Multivariable analysis revealed that the presence of ED was significantly associated with a high percentage of crossing capillaries (odds ratio: 2.70, 95% confidence interval: 1.05–6.90, p < 0.05).

This study is the first to demonstrate that patients with ED exhibit increased morphological abnormalities in nailfold capillaries compared to healthy individuals. The findings suggest that increased crossing capillaries may serve as an early visual marker of microvascular damage in ED patients. Given the non-invasive and easily accessible nature of nailfold capillaroscopy, its use in routine clinical practice could facilitate early detection of microvascular impairment, potentially improving ED prevention and management.