Department of Neurosurgery, University of Wisconsin, Madison, WI, USA
3.1 Case Presentation
A 40-year-old male progressively developed a right foot drop 4 months ago. He has decreased sensation on the dorsum of the foot. This was associated with occasional mild low back pain and some outer leg pain. PMH significant for non-Hodgkin’s lymphoma treated by radiation and chemotherapy in full remission, asthma, and hypercholesterolemia. He works as a carpenter and does a lot of lifting. He has smoked a pack of cigarettes a day for 22 years and does not drink alcohol.
Examination of the right lower extremity: TA 1, EHL 2, extensor digitorum 2, eversion 2, inversion 5, and plantar flexion 5. There is decreased sensation on the dorsum of the first web space.
What is the differential diagnosis? What is the most likely diagnosis?
What tests would you order?
How would you treat this condition?
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The patient has a right foot drop . The differential diagnosis mainly includes an L5 radiculopathy or a peroneal neuropathy. Figure 3.1. The patient is unable to dorsiflex on the right side. The pattern of sensory loss on the dorsum of the first web space (grey area) is typical for a deep peroneal neuropathy. The patient also lost eversion but is able to plantar flex and invert. Inversion is typically lost in L5 radiculopathy (or more rarely high sciatic injury affecting both peroneal and tibial components). Since this patient has intact inversion, this is likely to be a peroneal neuropathy. Inversion is carried out by the tibialis posterior , which is supplied by the tibial n . Peroneal neuropathy can be caused by prolonged periods of knee hyperflexion (e.g., strawberry picking), casting, or rapid excessive weight loss .
Look for a Tinel’s sign along the peroneal n. The patient had a Tinel’s sign at the fibular neck. NCS : absent right superficial peroneal SNAP , conduction block above the fibular head for the right peroneal CMAP. EMG : denervation changes in right TA and peroneus longus (presence of fibrillations, absence of motor units), normal paraspinal muscles, and normal short head of biceps femoris . The abnormal SNAP together with the normal paraspinals rule out radiculopathy . The short head of biceps femoris is the last muscle supplied by the peroneal n in the thigh; this being normal localizes the lesion to below the knee, especially with the conduction block at the fibular head. MRI of the peroneal n ( Neurogram ): in order to rule out tumors or cysts.
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