Non-Invasive Triage of Bladder Outlet Obstruction and Detrusor Underactivity in Men With Lower Urinary Tract Symptoms: A Narrative Review and Conceptual Framework for Depth-Aware Multimodal Transcutaneous Testing.

INTRODUCTION: Differentiating bladder outlet obstruction (BOO) from detrusor underactivity (DU) remains a major unmet need in the management of lower urinary tract symptoms in men. Although pressure-flow urodynamics provide a definitive physiological classification, their invasiveness limits their widespread use. We reviewed why current non-invasive approaches have failed to achieve consistent clinical adoption and explored a pathway toward clinically useful pre-urodynamic triage.

METHODS: This hypothesis-generating narrative review synthesized evidence on non-invasive BOO/DU assessment, using suprapubic near-infrared spectroscopy (NIRS) as an illustrative example of transcutaneous physiological sensing. We examined the mechanistic, anatomical, and methodological factors that limit signal validity and considered how these constraints affect interpretation across modalities.

RESULTS: Current non-invasive approaches face limitations due to the physiological overlap between BOO and DU, differences in anatomical depth, contamination from abdominal wall activity during voiding, and variations in methodology. Advances in artificial intelligence may help with pattern recognition, but they cannot compensate for uncertainty regarding signal origin or physiological relevance. On the basis of these limitations, we propose a conceptual, non-validated depth-aware multimodal triage framework that combines real-time bladder localization, quality-controlled physiological sensing, and complementary non-invasive parameters. This framework needs prospective validation before clinical implementation.

CONCLUSIONS: Persistent difficulty of non-invasive BOO/DU differentiation reflects the limitations of the prevailing diagnostic paradigm rather than the shortcomings of any single technology. A depth-aware multimodal approach is not intended to replace urodynamics but may support pre-urodynamic triage, reduce diagnostic uncertainty, and enable more selective use of invasive testing. This framework should be regarded as a hypothesis-generating model for future validation rather than as a clinically implementable diagnostic tool.