Pathophysiology and differential diagnosis of benign prostatic hypertrophy

Although the symptoms of benign prostatic hyperplasia are usually attributed to simple mechanical obstruction of the prostatic urethra by an enlarged prostate gland, the pathophysiology of this common urologic disorder actually involves multiple factors. These include abnormalities of detrusor function, neuromuscular abnormalities of the prostatic urethra, and sensory abnormalities of the bladder wall. Detrusor abnormalities include impaired detrusor contractility and involuntary detrusor contractions (detrusor instability or detrusor hyperreflexia). Neuromuscular abnormalities of the prostatic urethra are characterized by alpha-adrenergic overactivity which causes outlet obstruction or by alpha-adrenergic hypoactivity which may result in urinary incontinence. Sensory abnormalities of the bladder wall include hypersensitivity (sensory urgency) or hyposensitivity which can lead to overdistention and urinary retention. The diagnostic evaluation of patients with clinical prostatism must take these factors into account. Of particular importance is the recognition that a decreased urinary flow rate and/or increased postvoid residual urine volume may be caused by either bladder outlet obstruction or impaired detrusor contractility. Routine urodynamic studies do not permit a distinction between these two entities, but video/detrusor pressure/uroflow studies are usually definitive.