Neurology India, Vol. 58, No. 2, March-April, 2010, pp. 303-305
A rare cause of foot drop after radiofrequency ablation for varicose veins: Case report and review of the literature
R Shiva Kumar, Malini Gopinath
Department of Neurology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala, India
Correspondence Address: R Shiva Kumar, Department of Neurology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum - 695 001, India, email@example.com
Date of Acceptance: 15-Oct-2009
Code Number: ni10076
AbstractThe treatment option for varicose veins (VV) is mainly surgery both open and minimally invasive. Even though mortality and major morbidity are rare with surgery, minor neurological complications like cutaneous nerve injuries remain a common problem. Involvement of major branches of sciatic nerve is extremely a rare complication of radiofrequency ablation (RFA), the other treatment option for VV. To the best of our knowledge, injury to both peroneal and tibial nerves has not been reported following RFA procedure. We report a very rare complication of sudden onset foot drop after RFA for VV. Lack of knowledge of such symptoms may lead to misdiagnosis and electrodiagnostic and magnetic resonance imaging studies can help in correct diagnosis.
Keywords: Radiofrequency ablation, varicose veins, ultrasound
Foot drop, not an uncommon condition, is a distressing symptom associated with falls and injuries. The most common cause is peroneal neuropathy at the head of the fibula and include lumbar plexopathies, L5 radiculopathy, partial sciatic neuropathy anterior horn cell disease.  Electrodiagnostic studies are useful adjuncts in localizing the site of injury and also help in assessing the degree of injury and recovery.  In varicose veins (VV) treatments aim at removing the superficial venous system either through surgery, endovenous ablation or sclerotherapy ablation and very occasionally these may be associated with neurological complications.  Here, we report an uncommon complication, foot drop following radiofrequency ablation (RFA) for VV.
A 55-year-old female presented with sudden onset weakness of the left leg following ultrasonography (USG)-guided endovenous RFA under local anesthesia of both short and long saphenous veins. She noticed numbness over the left foot followed by weakness without neurolgic pain within few hours of the procedure. Over the next three weeks, her sensory symptoms partially improved but weakness persisted and she was referred to our center for further evaluation. Neurological examination showed grade 1/5 power in the left ankle dorsiflexors, grade 2/5 power in the evertors of the foot, grade 4/5 power in the foot plantar flexion and grade 4/5 power in the biceps femoris muscle. Hip abduction, adduction, extension and knee extension was normal. Left ankle reflex was absent. There was a clear sensory disturbance over the dorsum of the foot, first dorsal web space, lateral knee and posterior calf on the left side. There were multiple well-healed scars related to the procedure over the left lower limb.
Conventional radiographs of the lumbosacral spine were normal. Magnetic resonance imaging (MRI) of the lumbosacral plexus and thigh (sciatic nerve) was normal. Ultrasound examination of the sciatic nerve and its branches at the popliteal fossa did not show any pathology. Electrodiagnostic studies: left peroneal nerve was not elicitable, prolonged motor latency with marginally reduced compound motor action potential (CMAP) from left tibial nerve, no recordable sensory action potential from left sural and superficial peroneal nerves [Table - 1]. Needle electromyography (EMG) showed acute denervation in the tibialis anterior, medial head of gastronemius, peroneus longus, tibialis posterior and flexor digitorum longus muscles [Table - 2], indicating injury to both tibial and common peroneal nerves probably at the site of or after the origin from the sciatic nerve. The patient was fitted with a modeled ankle orthosis and was continued on regular physical therapy with only minimal improvement at 1 year follow-up.
For patients with VV, radiofrequency endovenous ablation, a newer procedure, is less invasive and has a fewer complications thatn surgery. RFA works by thermal destruction and causes irreversible local tissue damage. Radiofrequency energy is delivered through a special catheter with deployable electrodes at the tip: the electrodes touch the vein walls and deliver energy directly into the tissues without coagulating blood. 
Neurological complications usually occur in the form of local paresthesiae from perivenous nerve injury, but are usually temporary. Rarely, injury to the common peroneal nerve, sural or saphenous nerve have been reported as complications following RFA.  The occurrence of foot drop shortly after the procedure in our patient indicates injury either to the common peroneal nerve or a more proximal focal lesion. However, patients with foot drop sometimes pose a difficult diagnostic challenge for two reasons: first, partial involvement of the common peroneal nerve may produce highly variable degrees of weakness and sensory loss in the muscles and skin supplied by the nerve and second, the nerve lesion lies more proximally than the common peroneal nerve.
Careful clinical examination and electrodiagnostic studies usually help in localizing the lesion.  Electrodiagnostic studies are a valuable extension of the clinical examination in evaluating patients with foot drop and they also help in predicting prognosis.  When more proximal lesions are suspected, a very useful strategy is to perform needle EMG examinations of the lumbar paraspinal, gluteal and hamstring muscles. Often, the two most important muscles to test are the short head of the biceps femoris and the tibialis posterior muscles. Imaging is indicated in patients with peroneal neuropathy with no apparent cause or no improvement or worsening. Computed tomography (CT) scanning is excellent for detecting large soft tissue masses in this area. MRI is even more sensitive for demonstrating the range of intrinsic and extrinsic mass lesions involving the peroneal nerve.
The mechanism of peripheral nerve damage after RFA for VV is unclear. Similar such complication, phrenic nerve injury after RF at the pulmonary vein orifice for atrial fibrillation and trigeminal nerve after RF for trigeminal neuralgia have been reported.  However, the damage can be either due to thermal injury or local compression of nerves either due to edema or ecchymoses. The proposed mechanisms for nerve injury are direct damage due to current-mediated electromagnetic effects, alteration of the membrane potential producing subsequent conduction block and microlesion formation or electroporation of nerve cells resulting in axonal coagulation and necrosis. 
The sciatic nerve and its distal branches, tibial and peroneal, are in close proximity to the terminal part of the superficial saphenous vein (SSV) near the sapheno-popliteal junction (SPJ), especially when the SSV is dilated due to venous incompetence [Figure - 1]. Both radiofrequency ablation and endovenous laser treatment involve considerable heating of the vein wall and can cause damage to the tissues surrounding the vein. The chances of injury to the sciatic nerve or its branches is high if they lie close to the sapheno-popliteal junction in the popliteal fossa.  Risk factors for injury to the nerves are tissue temperatures during ablation, direct injury to the nerves, anatomical course of the nerve in relation to the surrounding structures and the thickness of the tissue barrier between the catheter tip and the nerves. Ultrasound examination of the popliteal fossa before endovenous ablations of VV aids identification of sciatic nerve varices, anatomical relations of the sciatic nerve and its branches and position of the SPJ.  Once the relationship of the nerve and its branches is defined, necessary precautions can minimize the risk of injury to the surrounding nerves. Hence, we emphasize the need for routine preprocedural USG in all patients selected for RFA or laser treatment for VV.
In summary, postprocedural tibial and common peroneal neuropathy after RFA is rare, but it may occur. However, no definite guidelines or recommendations exist for the exact dose and duration of RF exposure at these vulnerable sites. Electrodiagnostic studies should be used routinely in all cases of acute neuropathies as they help in localizing the lesion site and predicting the severity and prognosis of the disease, and MRI and CT studies can rule out a mass lesion.
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