Introduction
Foot drop is common symptoms that a physiatrist could meet at electrodiagnostic lab. To confirm the affected region, electromyogram (EMG) is significant and useful. The lesion would be exist from the anterior horn cell at the lumbar spinal cord through lumbosacral plexus to peroneal nerve. The peroneal nerve palsy could be caused by traumata or occur insidiously by mass lesion or metabolic syndromes.
In this case, peroneal nerve palsy at or around fibular head was diagnosed by EMG at emergency room. The physition could intervene early which is fundamental to prevent permanant gait abnormality.
Case Report
60-year-old woman visited the emergency room on July 7th, 2017. She complained of the right foot drop 3 days ago. She had medical history of diabetes mellitus and Graves’ disease and had both total knee replacement 5 years ago. There was no history of trauma. The primary physition and the neurosurgeon suspected lumbar radiculopathy, so ordered the magnetic resonance imaging of lower back. There was no evidence of disc herniation or root compression. Therefore she was referred to the deparment of rehabilitation medicine for an EMG test.
On the manual muscle test (MMT) , the right ankle dorsiflexion was T, ankle eversion was P, great toe extension was T and 2nd to 5th toes were T grade. There was a palpable mass around the right fibular head and Tinnel sign was positive. On EMG, compound muscle action potentials (CMAPs) of the deep peroneal nerve stimulated at the ankle and around the fibular head were normal. However, the CMAP stimulated at the popliteal fossa showed decreased amplitude. Findings were compatible with the conduction block of right peroneal nerve (Fig 1). On ultrasonography, the cystic mass was observed around the right fibular head (Fig 2).
Excision of the cyst was delayed to 10 days after the diagnosis, July 24th, 2017, due to the risk of thyrotoxicosis and poor control of blood glucose level. In the operation field, bulging cyst was found on the fascia and the cystic mass inside the nerve sheath along the common peroneal nerve. After dissecting the cyst from the nerve, the atrophy of the nerve was not seen.
On the follow-up EMG was done on July 24th and August 10th 2017 showed improvement of interference of motor units of the tibialis anterior muscle (Fig 2, 3). The MMT of ankle dorsiflexion improved as F grade compared with T grade at first.
Discussion
Since the ganglion cyst in the lower extremity is very rare, the diagnosis of the ganglion cyst around the fibular head in this case would have been very difficult. However, proper history taking, physical examination and the EMG made the diagnosis exactly. It made possible the early intervention to relieve the symptom and the patient was able to recover motor weakness. This case demonstrated usefulness of the EMG in the emergent situation such as sudden motor weakness. |
