Patient has bilateral triceps weakness with a normal cervical‑spine MRI; what are the appropriate next diagnostic tests and management steps?

Bilateral Triceps Weakness with Normal Cervical MRI: Next Steps

Order EMG/nerve conduction studies immediately to evaluate for peripheral nerve pathology, and strongly consider CT myelography if EMG is non-localizing, because a normal cervical MRI does not exclude clinically significant nerve root or cord pathology—particularly when objective motor deficits are present.

Why a Normal MRI Does Not Rule Out Pathology

• MRI misses approximately 12% of surgically significant cervical radiculopathy lesions, achieving only 88% diagnostic accuracy even in optimal conditions. 1, 2, 3

• Bilateral triceps weakness (C7 radiculopathy) with a normal MRI suggests either:

  • Subtle nerve root compression below MRI resolution
  • Preganglionic nerve root avulsion (better seen on CT myelography) 4
  • Peripheral nerve pathology (requires electrodiagnostic testing)
  • Early inflammatory/demyelinating process not yet visible 5, 6

• Compressive myelopathy can present with isolated lower motor neuron findings before developing classic upper motor neuron signs, and early cord compression may show minimal or no signal change on MRI. 5, 7, 8

Immediate Diagnostic Algorithm

Step 1: Electrodiagnostic Testing (First Priority)

• Order EMG and nerve conduction studies of bilateral upper extremities to:

  • Localize the lesion to nerve root, plexus, peripheral nerve, or anterior horn cell 4
  • Differentiate C7 radiculopathy from radial neuropathy or other peripheral causes
  • Identify subclinical involvement of other myotomes suggesting a central process

• EMG findings guide all subsequent imaging decisions—if EMG confirms bilateral C7 radiculopathy, proceed immediately to Step 2. 1, 3

Step 2: Advanced Imaging (If EMG Confirms Radiculopathy)

• CT myelography is the next appropriate study when MRI is normal but clinical/EMG findings indicate nerve root pathology, achieving 81% diagnostic accuracy for radiculopathy versus only 50% for plain CT. 1, 3

• CT myelography provides superior visualization of:

  • Preganglionic nerve root avulsions (which MRI frequently misses) 4
  • Foraminal stenosis and bony nerve root compression at higher spatial resolution than MRI 1
  • The thecal sac and small nerve roots in cases where MRI is equivocal 1, 3

• Be aware that CT myelography carries procedural risks: approximately 30% of patients experience unexpected adverse reactions to intrathecal contrast, and 14% report maximum pain scores of 10/10 during injection. 1

Step 3: Consider Inflammatory/Demyelinating Workup

• If EMG shows widespread denervation or upper motor neuron signs develop, obtain:

  • Lumbar puncture for cell count, protein, oligoclonal bands, and NMO-IgG antibody 5, 6
  • Serum aquaporin-4 and MOG antibodies 6
  • Brain MRI to evaluate for demyelinating lesions 6

• Compressive myelopathy can mimic transverse myelitis with long T2 hyperintense lesions, but gadolinium enhancement in compression is localized to the level of maximum stenosis, whereas inflammatory myelitis shows extensive enhancement. 5

• Cervical myelopathy may present with only lower extremity symptoms in atypical cases, so absence of hand clumsiness does not exclude cord pathology. 7

Critical Pitfalls to Avoid

• Do not assume a normal MRI excludes significant pathology when objective motor weakness is present—MRI has a 12% false-negative rate for radiculopathy. 1, 2, 3

• Do not order plain CT as a substitute for CT myelography—plain CT detects only 50% of radiculopathy lesions versus 81% for CT myelography. 1, 3

• Do not empirically treat with corticosteroids before excluding compressive pathology—one case series showed patients with compressive myelopathy initially misdiagnosed as transverse myelitis responded poorly to steroids but improved dramatically after surgical decompression. 5

• Do not overlook venous hypertensive myelopathy—rare cases of progressive myelopathy with centromedullary T2 hyperintensity and flow voids on dorsal cord surface have been reported even with "normal" baseline imaging, improving after decompression surgery. 8

Management Pending Workup

• Avoid cervical manipulation or aggressive physical therapy until nerve root or cord pathology is definitively excluded. 4

• Monitor closely for progression of weakness, development of upper motor neuron signs (hyperreflexia, Babinski, clonus), or bowel/bladder dysfunction—any of these warrant urgent repeat imaging and neurosurgical consultation. 7

• If symptoms are rapidly progressive or bilateral motor deficits worsen, proceed directly to CT myelography without waiting for EMG results, as this pattern suggests evolving cord compression requiring urgent surgical evaluation. 4, 5, 8