Femoral Mononeuropathy

Femoral mononeuropathy in the agricultural setting may be caused primarily by compression of the nerve as it passes through the psoas muscle and through the iliopsoas groove. This compression may be caused by excessive flexion, abduction, and external rotation of the hip, which occur relatively commonly in workers whose daily routine requires manipulation of heavy objects. Blunt trauma to the nerve is also common, as is resulting hemorrhage that exacerbates the degree of neuropathy (41).

Patients may present with "knee buckling," another manifestation of muscle weakness that develops relatively rapidly. Paresthesias are rare but possible, especially if there is involvement of the lateral femoral cutaneous branch (meralgia paresthetica); in many cases numbness of the medial thigh and the calf is also present. Decreased patellar reflex and quadriceps wasting are expected in these patients, as there may be slow and often partial involvement of the iliopsoas (41).

Evaluation for femoral nerve dysfunction includes NCSs and needle EMG. If an NCS is performed, it should include sensory studies of the saphenous nerve and motor studies of the femoral nerve, while EMG should show neuropathic changes in the quadriceps and possibly iliopsoas. The EMG should be performed in cases of suspected involvement of the lateral femoral cutaneous nerve, as it is the easiest modality that allows ruling out upper lumbar radiculopathy (41).

Peroneal mononeuropathy is common and may be caused by prolonged sitting in a slightly tilted position, as, for example, in a tractor driver's seat or airplane seat, especially in patients who cross their legs or fold the left leg underneath while pushing the pedals with their right foot. Squatting, especially in persons of thin stature, is a known risk factor, while obesity is emerging as the most commonly overlooked source of peroneal nerve compression (40).

In cases of peroneal mononeuropathy, patients present with foot drop that often spares plantar flexion and foot inversion, night cramps ("charley horse," especially early in the course of the disease), and sensory manifestations such as neuropathic numbness and neuropathic tingling. The gait may be either high-stepping or foot-slapping or both. Asking patients to walk on their heels may aid in diagnosis as weakness of foot dorsiflexion will become more obvious. Differentials include generalized neuropathy, chronic inflammatory demyelinating neuropathy, and L5 radiculopathy. All of these can present with a foot drop but usually spare the foot inverters (40).

Both NCS and EMG are recommended in these patients. The NCS may indicate peroneal nerve abnormalities, especially in the presence of axonal damage, which manifests as a smaller compound muscle action potential. The NCS also allows differentiation among mononeuropathy, vasculitic mononeuritis multiplex, and generalized polyneuropathy of other (e.g., diabetic) etiology.

The EMG is especially valuable in localizing the compression/lesion area(s) and in differentiation between L5 radiculopathy and peroneal mononeuropa-thy. The EMG may also suggest involvement of the thigh muscles, which may necessitate an MRI study of the thigh to rule out mass lesions (40).

Management

Treatment is dependent on the etiology and location of the lesion. Most patients with lower extremity mononeuropathies should be treated conservatively with physical therapy, avoidance of motions and postures that caused or contributed to their condition (e.g., excessive hip abduction and external rotation in femoral involvement, leg crossing or folding in a "semi-lotus" position in peroneal disorder), and specific braces. Surgery for decompression may be indicated but may not lead to a complete reversal of symptoms. Pain may be effectively controlled with analgesics and, more recently, anticonvulsants, which are rapidly becoming a standard part of the armamentarium. In cases of neuropathy due to diabetes or vasculitis, immunomodulating therapy may be attempted (39,40).

Occupational therapy and physical therapy are always desired, as are patient education and support programs. Unfortunately, the availability of such programs and treatment modalities may be very limited.

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