A 55-year-old man presents with irritative and obstructive urinary symptoms. What is the likely diagnosis?

The presentation of irritative and obstructive urinary symptoms in a 55-year-old man is most consistent with benign prostatic hyperplasia (BPH). BPH is a common condition in older males, characterized by the enlargement of the prostate gland, which results in urinary symptoms due to obstruction of the urethra.

Irritative symptoms may include increased frequency of urination, urgency, and nocturia, while obstructive symptoms can manifest as a weak urinary stream, difficulty starting urination, or a sensation of incomplete bladder emptying. Given the age of the patient and the specific symptomatology, BPH emerges as the most likely diagnosis.

Other conditions, such as prostate cancer and urinary tract infection, can present with similar symptoms, but they typically have additional features or risk factors that would guide further evaluation prior to being diagnosed. Bladder stones could also cause these symptoms, but they are less common in this demographic and often associated with additional findings such as hematuria or significant pain. Therefore, the combination of age, symptoms, and the nature of their presentation strongly supports benign prostatic hyperplasia as the diagnosis in this case.