MRI of the Spine is the First Diagnostic Test to Order
For a patient with prostate cancer history presenting with decreased left leg strength, order an urgent MRI of the entire spine immediately to evaluate for metastatic spinal cord compression. This is a neurological emergency where early detection is critical, as the neurological status before treatment is the major determinant of outcome 1, 2.
Why MRI is the Definitive First Test
MRI detects both overt and occult spinal cord compression in 27.3% of prostate cancer patients with no functional neurological deficit, making it essential even when weakness is the only presenting symptom 1.
MRI is superior to all other imaging modalities for diagnosing spinal cord compromise, including CT and bone scintigraphy, because it directly visualizes the spinal cord, epidural space, and thecal sac 3.
The American College of Radiology explicitly recommends against PET-CT as an initial test for acute neurologic emergencies, as it does not provide adequate detail of spinal cord compression and delays definitive diagnosis 4.
Clinical Context Supporting Urgent MRI
Unilateral leg weakness in prostate cancer is highly concerning for epidural metastatic disease causing nerve root compression or early cord compression, which occurs in 7% of men with prostate cancer 2.
Back pain is present in 79% of patients before neurological symptoms develop (average 60 days prior), but 21% present with neurological deficits without preceding pain 5.
Extensive bone metastases and back pain are the strongest predictors of radiological spinal cord compromise on multivariate analysis (P=0.047 and P=0.012 respectively) 1.
Critical Time-Sensitive Actions After Ordering MRI
While awaiting MRI results, immediately initiate:
High-dose corticosteroids (typically dexamethasone 10-16 mg IV/PO) to reduce spinal cord edema 2, 6.
Continue existing androgen suppression if the patient has castration-resistant disease 4.
Initiate androgen deprivation therapy urgently (bilateral orchiectomy or LHRH agonist) if the patient is hormone-naive, as these patients have dramatically better outcomes 4.
Why Other Tests Are Inappropriate as First-Line
Bone scintigraphy, while recommended by EAU guidelines for detecting bone metastases in symptomatic patients 3, does not visualize the spinal cord or epidural space and cannot diagnose the cause of neurological deficits.
Plain radiographs should be performed alongside MRI but are insufficient alone, as they miss epidural disease and early cord compression 2.
CT of the spine is inferior to MRI for bone metastasis diagnosis and follow-up, and misses early spinal cord involvement 7.
Common Pitfalls to Avoid
Never delay MRI to obtain bone scan first in a patient with neurological symptoms—this is a neurological emergency requiring immediate cord visualization 4, 2.
Do not assume normal ambulation excludes cord compression—27.3% of patients harbor occult or overt spinal cord compression without functional neurological deficit 1.
Image the entire spine, not just the symptomatic level—7 of 41 patients with radiological spinal cord compromise had involvement at multiple non-contiguous sites 1.
Recognize that 100% of ambulatory patients remain ambulatory with treatment, but only 83% of paraparetic patients regain ambulation, and paraplegic patients rarely recover—making early detection before progression absolutely critical 6.
Prognosis and Treatment Planning
Median survival after spinal cord compression is 4 months (range 2 weeks to 49 months), with paraplegic patients surviving only 3.9 months on average 5, 6.
Recurrent compression occurs in 27% of patients, emphasizing the need for prophylactic radiation of other vertebral metastases discovered on the initial MRI 6.
Definitive treatment is radiation therapy for most patients, with surgical decompression reserved for severe myelopathy, spinal instability, or neurological deterioration during radiation 2.