What is the most appropriate immediate action for a patient with stage IIIB small cell lung cancer (SCLC) presenting with new onset back pain and a normal initial neurological examination?

Immediate Management of New Onset Back Pain in Stage IIIB SCLC

The most appropriate immediate action is to obtain an MRI of the entire spine (Answer A), as this is the critical first step to rule out spinal cord compression, which is an oncologic emergency that can lead to irreversible paralysis if not diagnosed and treated promptly. 1

Clinical Reasoning

Why MRI Must Come First

• New onset back pain in a lung cancer patient is spinal cord compression (SCC) until proven otherwise. In patients with known lung cancer presenting with new back pain, sagittal T1-weighted MRI of the entire spine is the recommended initial diagnostic test, even when the neurological examination is normal 1.

• Normal neurological exam does not exclude SCC. At presentation, 90% of patients with SCC have pain (local and/or radicular), but up to 50% may still be ambulatory without obvious neurologic deficits initially 1. The natural history of untreated SCC is relentless progression to paralysis, sensory loss, and sphincter dysfunction 1.

• Time is critical for preserving function. Patients who develop paralysis either at presentation or after treatment have much shorter life expectancy than ambulatory patients, and the deterioration is devastating and difficult to manage 1. The consequences of cord compression are so severe that imaging should be done emergently 1.

Why Not High-Dose Corticosteroids First (Answer D)

While this seems logical, the guidelines are nuanced:

• Corticosteroids should be given when there is "significant clinical suspicion" of SCC, ideally prior to radiographic confirmation 1. However, the key phrase is "significant clinical suspicion."

• With a normal neurological examination and only 12 hours of back pain, the clinical picture does not yet constitute "significant" suspicion requiring empiric high-dose steroids before imaging 1.

• The guideline specifically states that if MRI is found to be negative, de-escalation of steroid treatment can occur rapidly 1, suggesting that imaging confirmation should guide steroid initiation when the clinical picture is ambiguous.

• High-dose dexamethasone (96 mg/day) carries significant toxicity (29% side effects, 14% serious including GI perforation, bleeding, and one fatal ulcer) 1, making empiric treatment without imaging confirmation inappropriate when the exam is normal.

The Correct Algorithmic Approach

1. Immediate MRI of entire spine (within hours, not days) 1

2. If MRI confirms epidural spinal cord metastases:

   • Non-symptomatic (normal neuro exam): Prompt high-dose dexamethasone and radiotherapy 1
   • Symptomatic with good performance status: Neurosurgical consultation for immediate surgery followed by radiation 1

3. If MRI is negative: Evaluate for other causes of back pain (bone metastases, vertebral compression fracture, musculoskeletal pain) 1

Common Pitfalls to Avoid

• Do not delay imaging to start steroids empirically when the neurological exam is normal. The risk of steroid toxicity outweighs the benefit when SCC is not yet confirmed 1.

• Do not wait for neurological symptoms to develop before obtaining MRI. By the time paralysis occurs, the prognosis for recovery is poor 1.

• Do not image only the symptomatic spinal level. The entire spine must be imaged because multiple levels of involvement are common 1.

• Do not dismiss back pain as "just bone metastases" without imaging. SCC can present with pain alone before neurological deficits develop 1.

Answer: A (MRI)