Differential Diagnosis and Management
Primary Recommendation
This patient requires urgent MRI of the left forearm and brachial plexus to evaluate for peripheral nerve pathology, as the acute neurological deficit with normal brain and cervical spine imaging strongly suggests a peripheral nerve lesion related to the prior stab wound. 1, 2
Differential Diagnosis
Most Likely: Peripheral Nerve Pathology
Delayed peripheral nerve complications from the prior stab wound:
- Neuroma formation causing acute nerve dysfunction (most likely given the 7-year interval and acute presentation) 1
- Nerve entrapment from scar tissue or fibrous bands developed over time 1
- Delayed nerve compression from chronic changes at the injury site 1
- Spontaneous intraneural hemorrhage within a pre-existing nerve lesion 3
The complete loss of finger flexion and extension (0/5) localizes to either:
- Median and ulnar nerve dysfunction (if both flexion and extension affected across all fingers) 1
- Posterior interosseous nerve (if primarily extension deficit) 1
- Anterior interosseous nerve (if primarily flexion deficit) 1
Less Likely but Must Exclude:
Brachial plexus pathology:
- Delayed brachial plexus injury from the original trauma 1, 2
- Thoracic outlet syndrome with acute decompensation 1
Vascular complications:
- Compartment syndrome (though typically presents with pain) 1
- Vascular injury with delayed ischemic neuropathy 4
Spinal cord pathology (less likely given normal cervical MRI):
- Occult spinal cord lesion not visualized on initial MRI 4, 1
- Delayed post-traumatic syrinx (though 7 years is unusual timing) 5, 6
Diagnostic Algorithm
Immediate Imaging (Within 24-48 Hours):
1. MRI of the left forearm and brachial plexus without contrast 1, 2, 3
- Include T2-weighted sequences to identify nerve edema or masses 1
- Include T1-weighted sequences to characterize tissue characteristics 1
- Include STIR sequences for detecting inflammation or fluid collections 3
- Rationale: MRI is superior for soft tissue evaluation and can detect neuromas, nerve compression, or intraneural pathology that would explain the acute deficit 1, 2
2. If forearm MRI is unrevealing, obtain MRI of the cervical spine with contrast 1, 2
- Despite normal initial cervical spine MRI, contrast may reveal subtle inflammatory or vascular lesions 2
- Evaluate for delayed spinal cord pathology including syrinx or myelomalacia 5, 6
- Rationale: Persistent unexplained neurological deficits warrant contrast-enhanced imaging to exclude occult pathology 1, 2
Electrodiagnostic Studies:
Nerve conduction studies and EMG of the left upper extremity (can be performed concurrently with imaging workup)
- Localizes the level of nerve injury (peripheral nerve vs. plexus vs. root) 1
- Differentiates axonal from demyelinating pathology 1
- Timing consideration: EMG changes may not appear for 2-3 weeks after acute injury, but nerve conduction studies can provide immediate information 1
Management Based on Findings
If Peripheral Nerve Lesion Identified:
Surgical exploration and neurolysis if:
- Compressive lesion (neuroma, scar tissue) identified on MRI 7
- Progressive neurological deterioration 7
- No improvement after 3 months of conservative management 7
Conservative management if:
- Mild nerve compression without complete disruption 7
- Includes hand therapy, splinting, and serial examinations 7
If Spinal Cord Pathology Identified:
Urgent neurosurgical consultation 7, 5
- Surgical decompression if cord compression identified 7, 5
- Critical caveat: Even with normal initial imaging, delayed cord pathology can occur and requires aggressive management 7, 5
Critical Pitfalls to Avoid
1. Assuming the normal brain and cervical spine MRI excludes all central pathology 4, 1
- MRI can miss subtle cord lesions, particularly without contrast 1, 2
- Peripheral nerve pathology is far more likely given the history, but central causes must be definitively excluded 1
2. Delaying imaging of the forearm/brachial plexus 1, 2
- The 7-year interval between injury and acute deficit suggests a peripheral complication that requires urgent evaluation 1
- Early identification of compressive lesions allows for timely surgical intervention if needed 7
3. Attributing symptoms to "old injury" without investigation 7, 5
- Acute neurological deficits always require explanation, regardless of remote trauma history 1, 7
- Delayed complications from peripheral nerve injuries can present years after the initial trauma 1
4. Failing to obtain contrast-enhanced imaging if initial studies are unrevealing 1, 2
- Contrast can reveal inflammatory, infectious, or vascular pathology not visible on non-contrast sequences 2
- In patients with persistent unexplained deficits, contrast-enhanced MRI leads to management changes in 76% of cases 2