A 72-year-old man visits the doctor due to complaints of severe low back pain for the past week as well as urinary and fecal incontinence for the last two days. He is currently receiving chemotherapy for transitional cell carcinoma of the bladder. Vital signs are within normal limits. On physical examination, there is tenderness over the lumbar spine at L4-L5 and reduced sensation below this level with numbness in his legs. A rectal examination shows a decreased sphincter tone, and his prostate is generally enlarged.
B) MRI of the spine
A patient with a diffusely enlarged prostate in the setting of new neurologic symptoms, likely has prostate cancer, which often metastasizes to the lumbar spine. One of the initial presentations of metastatic prostate cancer is low back pain, caused by metastasis to the lumbar spine. MRI of the spine is indicated for the evaluation of acute onset neurological deterioration. Cauda equina syndrome occurs from acute compression of the cauda equina nerve roots in the lumbosacral spinal canal, most commonly from an acute disc herniation or a traumatic or pathologic vertebral column fracture. This results in bilateral lower extremity weakness, loss of deep tendon reflexes, bowel or bladder dysfunction (e.g., overflow urinary incontinence), and saddle anesthesia. Emergent MRI of the lumbosacral spine is indicated to investigate the cause of cauda equina syndrome and to determine the necessity of surgical decompression or other acute interventions.
Answer choice A: Cystourethrography, is incorrect. Cystourethrography can be helpful in the diagnosis of urinary tract abnormalities, such as urethral stricture or urethral trauma, which can present with urinary retention.
Answer choice C: Measurement of serum prostate-specific antigen concentration, is incorrect. The PSA test is used as a tumor marker to monitor prostate cancer. While this patient likely has prostate cancer that has metastasized to bone, and measurement of the PSA will be indicated, this patient's signs and symptoms of cauda equina syndrome are a surgical emergency, and an MRI of the spine should be the next diagnostic step.
Answer choice D: Renal ultrasonography, is incorrect. Renal ultrasonography is indicated in patients who are suspected to have postrenal obstruction causing hydronephrosis, such as nephrolithiasis or an enlarged prostate. This patient's clinical presentation is more consistent with a spine pathology.
Answer choice E: Urine culture, is incorrect. Urine culture is helpful in the diagnosis of urinary tract infection, which can present with urinary symptoms such as dysuria, frequency, and urgency. It would not cause spinal tenderness, numbness, or decreased sphincter tone, which are more indicative of a spine pathology.
Key Learning Point
Prostate cancer often metastasizes to the lumbar spine. Cauda equina syndrome occurs from acute compression of the cauda equina nerve roots in the lumbosacral spinal canal and should be emergently evaluated with an MRI of the spine.
