12/5/2018 12:19:12 PM
Seeking assistance understanding and localizing a lesion in a patient
I was wondering if you could help me understand and localize a lesion so as to explain the findings below in a 42 year old woman who is 1 year s/p a MVC with an associated pelvic ring FX and right foot drop. On physical examination she has a clear inability to dorsiflex the right foot against gravity and similarly can’t evert this foot either. When she tried these maneuvers, I can, however, feel some muscle contraction. She is also numb on the dorsum of her foot, but there is a clear well healed scar 7 cm in length just medial to the lateral malleolus extending from just inferior to the lateral malleolus vertically. Her sensation along the lateral margin of her foot is relatively intact but decreased compared to the other side. The patient has no difficulty extending her knee and I cannot overcome her ankle plantar flexion. Hip flexion is normal as is hip extension and leg external/internal rotation.
On needle EMG of the right lower limb, there are PSW/Fibs easily observed in the following muscles with motor units, but displaying a somewhat neurogenic recruitment pattern: gastrocnemius, tibialis anterior, peroneus longus, flexor digitorum longus, short and long head of the biceps femoris, semimembranosus. There were fewer motor units recruited in the fibular compared to tibial innervated muscles. The following muscles revealed no abnormalities at rest with normal recruitment: gluteus maximus, tensor fascia lata, vastus medialis, and adductor longus. At this point, the patient declined any further needle examination.
Of note, the patient had considerable instrumentation of her L/S spine following the trauma and would not permit any needle assessment of her back.
The sural SNAP on the affected limb had a latency of 3.9 ms with an amplitude of 7 uV and the superficial fibular sensory response was absent. The tibialis anterior CMAP revealed a below fibular head magnitude of 2 mV with an above fibular head amplitude of 1.6 mV. The patient now requested termination of any further needle insertions or nerve stimulation.