Lesion Location: Lower Cervical Spinal Cord (C8-T1 Level)
The clinical presentation strongly suggests a lesion affecting the lower cervical spinal cord at the C8-T1 level, most consistent with central cord syndrome or a focal myelopathy affecting the anterior horn cells and lateral columns at this level.
Clinical Reasoning
The pattern of deficits points to a spinal cord lesion rather than a peripheral nerve injury:
Motor Findings Analysis
- Finger extension weakness (all fingers): C7-C8 innervation via radial nerve, but the pattern suggests anterior horn cell involvement
- Weak finger abduction: Dorsal interossei (C8-T1, ulnar nerve)
- Weak thumb extension: C7-C8 (radial nerve - posterior interosseous branch)
- Partial thumb opposition preserved: C8-T1 (median nerve)
- Normal proximal function: Rules out more rostral cord lesions or brachial plexopathy
Sensory Findings Analysis
The sensory pattern is particularly revealing:
- 3rd finger tip: C7 dermatome
- 5th finger tip and hypothenar eminence: C8 dermatome
- This non-dermatomal, patchy distribution affecting multiple nerve territories (median and ulnar) in a hand-specific pattern is characteristic of central cord pathology rather than peripheral nerve or root lesions 1
Key Distinguishing Features
Why this is NOT a peripheral nerve lesion:
- Ulnar nerve lesions would spare thumb extension and affect the dorsal hand sensation 2
- Median nerve lesions wouldn't explain the 5th finger or hypothenar involvement
- Combined peripheral nerve injuries are extremely rare without trauma 3, 4
Why this IS a spinal cord lesion: The sudden onset with hand-predominant weakness affecting multiple myotomes, combined with patchy sensory loss crossing nerve territories, is pathognomonic for lower cervical cord pathology. The illustrative cases in recent guidelines demonstrate this exact pattern - hand weakness with preserved proximal strength and sensory changes in finger tips 1.
Most Likely Diagnosis: Central Cord Syndrome
Given the sudden onset and hand-predominant weakness, this presentation is most consistent with central cord syndrome affecting C7-C8-T1 levels 5. This condition:
- Disproportionately affects hand function over proximal arm strength
- Can occur from hyperextension injury, even minor trauma in patients with cervical stenosis
- Affects the central gray matter and medial portions of lateral columns where hand representation is located
- Produces patchy, non-dermatomal sensory loss 1, 5
Immediate Diagnostic Approach
Obtain urgent MRI cervical spine without and with contrast 6:
- Sagittal T2-weighted sequences to identify cord signal changes from C5-T1
- Axial T2-weighted images to assess for central cord involvement
- Look for cord compression, signal abnormality, or evidence of ischemia
- Flexion views may reveal dynamic compression if initial imaging is unrevealing 7
Critical imaging findings to identify:
- T2 hyperintensity in central cord at C7-C8-T1 levels
- Cord compression from degenerative changes
- Absence of longitudinally extensive lesions (>3 vertebral segments would suggest alternative diagnoses like transverse myelitis or neuromyelitis optica) 8
Important Caveats
Red flags requiring immediate neurosurgical consultation:
- Any progression of weakness
- Development of lower extremity symptoms
- Bladder/bowel dysfunction
- Respiratory compromise
Alternative considerations if MRI is negative:
- Cortical hand stroke affecting the motor cortex "hand knob" - though this would typically spare sensation 9
- Hirayama disease - but this has insidious onset, not sudden 10, 7
- Anterior spinal artery syndrome - but this typically includes bilateral findings and spinothalamic sensory loss
The sudden onset is the critical feature distinguishing acute cord pathology from chronic degenerative conditions and makes urgent imaging mandatory to exclude surgically correctable compression or acute ischemia.