Structural basis of geriatric voiding dysfunction. II. Aging detrusor: normal versus impaired contractility.

Little information on the structural norm of the aging detrusor is currently available. To gain insight into the pathophysiology of geriatric voiding dysfunction, detrusor biopsies were examined by electron microscopy to identify structural correlates of specific, urodynamically defined abnormalities of vesical function in 35 elderly subjects. Prospective urodynamic grouping of the subjects and segregation of the detrusor specimens by ultrastructural features were done independently and blindly. One structural pattern so identified, the dense band pattern, matched the urodynamic group with neither detrusor overactivity nor bladder outlet obstruction. This neither group included 11 women and 2 men 65 to 91 years old (mean age 76 years). Except for 2 patients with minimal stress incontinence, all were symptom-free. None of the patients had diabetes or a neurological deficit. Urodynamically, 10 patients had impaired and 3 had normal detrusor contractility. The dense band structural pattern was characterized by overall normal configuration of muscle cells and cell junctions, sarcolemma (muscle cell membrane) dominated by dense bands with depleted caveolae in interposed zones and slight widening of spaces between muscle cells with little-collagen content. Specimens from the 10 subjects with impaired contractility displayed, in addition, widespread degeneration of muscle cells and axons. The remaining 3 specimens, without degeneration, matched the subjects with normal contractility, who were continent and symptom-free. It is proposed that the dense band pattern represents the structural norm of aging detrusor, heralds a process of muscle cell de-differentiation in the detrusor accompanying natural aging, and may affect exchange and storage of ions involved in the excitation-contraction coupling mechanism of muscle cells through depletion of caveolae. Widespread degeneration of muscle cells and axons, superimposed on the dense band pattern, is proposed as the structural correlate of impaired detrusor contractility in the aging detrusor.