Introduction
Isolated femoral neuropathy is not a common disease and only a few cases have been reported to date. Most cases result from compression or traction injury during abdominal/pelvic surgery or labor. And the following causes were occasionally reported; complication of total hip arthroplasty, nerve ischemia during renal transplantation, hematoma formation from misguided femoral catheterizations, retroperitoneal hemorrhage from excessive anticoagulation. To our knowledge there have been no report on the idiopathic isolated femoral neuropathy that cannot be explained by the previously reported causes. Therefore, here, we report a case of idiopathic isolated femoral neuropathy.
Case report
A 51-year-old woman (157cm, 53kg) presented with subtle weakness of the right thigh for about 2 years. She had some difficulty only when going up and down the stairs. The patient had no underlying disease and no history of surgery or traumatic event.
Physical examination revealed right quadriceps muscle atrophy. On manual muscle test, strength in the right hip flexors was 3 of 5 and the knee extensors 3 of 5, ankle dorsiflexion 5 of 5, ankle plantarflexion 5 of 5. Deep tendon reflex was absent on the right and 2+ on the left. Hypesthesia on medial and lateral aspect of right lower leg was reported.
In nerve conduction study & electromyography (NCS & EMG), femoral motor conduction study showed decreased amplitude recording with surface electrodes from the right quadriceps (right 3.4 mV; left 12.5 mV). Sensory NCS of right saphenous nerve was absent; that of the left was normal (7.4 μV) (Table 1). On needle EMG, positive sharp waves and fibrillation potentials were present in iliopsoas and rectus femoris muscle. The motor unit action potentials (MUAP) of these muscles were large in appearance with reduced recruitment. The other muscles tested (right adductor longus, tibialis anterior, gastrocnemius, gluteus maximus, tensor fascia lata, lumbar paraspinal muscles) were normal. (Table 2) Interpretation was right femoral neuropathy with partial axonotmesis.
The magnetic resonance imaging (MRI) of the pelvis showed no evidence of femoral nerve compressive lesion, but revealed atrophy of femoral nerve innervated muscles. Other muscles such as adductor group, gluteal muscles and psoas were normal. (Figure 1.) The MRI of the lumbar spine showed mild bulging disc in L4-5 and annular fissure in L5-S1 without disc herniation or nerve root compression. On 1 year follow up, clinical symptom and neurologic sign were maintained without worsening.
This is the first case report of idiopathic isolated femoral neuropathy that cannot be explained by overt cause in relation to this condition despite of thorough diagnostic investigation.
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