200 Section - Can Signal Changes of the Denervated Muscles of MRI Determine the Site of Peripheral Nerve Injury?

Case Diagnosis: In case of foot drop with no typical electophysiologic findings, incomplete sciatic neuropathy rather than common peroneal neuropathy can be made by MRI findings of neuropathy such as high signal intensity and fatty degeneration of the innervated muscles.







Case Description: An 11-year-old girl visited us with right foot drop for two months, after sitting on a commode for more than half hour. Ankle dorsiflexer was 2-, otherwise 4 grade in the lower limb. No L/R discrepancies were observed in sensory examination and muscle stretch reflexes. NCS showed decreased amplitude of right superficial peroneal nerve with no abnormalities in motor nerve tests. F-wave and H-reflex were normal. Abnormal spontaneous activities were seen only in tibialis anterior with significant decrease of recruitment pattern in the ipsilateral biceps femoris, TA, and peroneus longus. Although initial diagnosis was right common peroneal neuropathy around the knee, current findings suggested more proximal lesion. Non-contrast-enhanced MRI revealed increased T1, T2 signals in BF, semimembranosus as well as fatty degeneration in TA and extensor digitorum muscles. Lumbar spine MRI showed no abnormalities. Incomplete sciatic neuropathy, more affecting peroneal division was diagnosed and PT and AFO was prescribed.

Discussions: In case of insufficient information on history taking from vulnerable subjects with near-normal NCS findings and disappearance of ASAs on needle EMG in subacute phase of peripheral nerve lesions with mild to moderate axonal injury, the determination of the exact site of the nerve lesion only with electrodiagnositc findings is often challenging.

Conclusions: In this case of foot drop in which no typical electrodiagnostic findings are seen, significant MRI findings of the neuropathy such as signal changes as well as fatty degeneration in the innervated muscles are very useful to determine the exact location of peripheral nerve injury.