A 60-year-old male presents with haematuria at the onset of micturition – the cause is –
**Core Concept**
The patient's symptoms suggest a condition affecting the lower urinary tract, specifically the urethra or bladder, during the process of urination. This condition is likely related to the urethral or bladder mucosa being irritated or damaged, leading to bleeding.
**Why the Correct Answer is Right**
The most likely cause of haematuria at the onset of micturition is a urethral stricture. A urethral stricture is a narrowing of the urethra caused by scarring or fibrosis, often resulting from trauma, infections, or iatrogenic injury. When the patient tries to urinate, the narrowed urethra causes resistance, leading to increased intra-urethral pressure. This increased pressure can cause the urethral mucosa to bleed, resulting in haematuria.
The mechanism of stricture formation involves the deposition of collagen and other extracellular matrix proteins, leading to fibrosis and narrowing of the urethral lumen. This process is often mediated by inflammatory cells and cytokines, which promote fibrosis and tissue repair.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a bladder tumor would more likely cause haematuria throughout the urine stream, rather than specifically at the onset of micturition.
**Option B:** This option is incorrect because an overactive bladder would cause symptoms such as urgency, frequency, and nocturia, but not necessarily haematuria.
**Option C:** This option is incorrect because a kidney stone would cause severe pain and hematuria, but the pain would be more likely to occur during the urine stream rather than specifically at the onset of micturition.
**Clinical Pearl / High-Yield Fact**
A urethral stricture can be a "silent" condition, with symptoms only appearing when the patient tries to urinate, making it essential to consider this diagnosis in patients presenting with haematuria at the onset of micturition.
**Correct Answer:** C.