The detrusor muscle: an innocent victim of bladder outlet obstruction.
OBJECTIVES: Benign prostatic hyperplasia (BPH) is considered a frequent cause of bladder outlet obstruction (BOO) and lower urinary tract symptoms (LUTS), although the physiopathologic mechanism through which BPH causes LUTS is not clear. Several morphologic and functional modifications of the bladder detrusor have been described in patients with BPH and could play a direct role in determining symptoms. The opinion is spreading that the enlarged prostates in patients with LUTS is nothing more than a mere bystander. Evidence has accumulated, however, supporting the role of BPH-related BOO as the direct cause determining bladder dysfunction and indirectly causing urinary symptoms. The present review addresses the bladder response to BOO, particularly focusing on the physiopathologic cascade that links obstructive BPH to bladder dysfunction. METHODS: A literature review of peer-reviewed articles has been performed, including both in vivo and in vitro studies on human tissue and animal model experiments. RESULTS: Epithelial and smooth muscle cells in the bladder wall are mechanosensitive, and in response to mechanical stretch stress caused by BOO, undergo modifications of gene expression and protein synthesis. This process involves several transduction mechanisms and finally alter the ultrastructure and physiology of cell membranes, cytoskeleton, contractile proteins, mitochondria, extracellular matrix, and neuronal networks. CONCLUSIONS: BOO is the initiator of a physiopathologic cascade leading to deep changing of bladder structure and function. Before being a direct cause of storing-phase urinary symptoms, the bladder is the first innocent victim of prostatic obstruction.