Idiopathic lumbosacral plexitis In addition to the diabetic type detailed earlier in the chapter, an idiopathic neuralgic amyotrophy or lumbosacral plexitis, analogous to the brachial variety, has been observed. Bradley and coworkers have recorded such cases and their paper can be referred to for the clinical details. After causing widespread unilateral or bilateral sensory, motor, and reflex changes in a leg, lumbosacral plexitis may leave the patient with dysesthesias as troublesome as those that follow herpes zoster (which also may occur at this level). Loss of sweating and warmth of the feet indicate interruption of autonomic fibers by lesions in peripheral nerves rather than in roots. The sedimentation rate may be elevated. Dyck and colleagues (2000) inferred an autoimmune basis from biopsy material and immunosuppressant drugs were possibly beneficial in 4 of 6 cases reported by Bradley and coworkers. The outcome is variable with complete recovery being uncommon.
Diabetic amyotrophy caused by involvement of the lumbar plexus and roots was discussed in an earlier section (“Diabetic Multiple Mononeuropathies and Radiculoplexus Neuropathy”).
Lateral Cutaneous Nerve of the Thigh (Meralgia Paresthetica)
This sensory nerve originates from the second and third lumbar roots and supplies the anterolateral aspect of the thigh from the level of the inguinal ligament almost to the knee. The nerve penetrates the psoas muscle, crosses the iliacus, and passes into the thigh by coursing between the attachments of the lateral part of the inguinal ligament to just anterior to the anterior superior iliac spine. Compression (entrapment) may occur at the point where it passes between the two prongs of attachment of the inguinal ligament.
Compression of the nerve results in uncomfortable paresthesias and sensory impairment in its cutaneous distribution, a common condition known as meralgia paresthetica (meros, “thigh”). Usually numbness and mild sensitivity of the skin are the only symptoms, but occasionally there is a persistent distressing burning pain. Perception of touch and pinprick are reduced in the territory of the nerve; there is no weakness of the quadriceps or diminution of the knee jerk. The symptoms are characteristically worsened in certain positions and after prolonged standing or walking. Occasionally, for an obese person, sitting is the most uncomfortable position. Obesity, pregnancy, and diabetes mellitus may be contributory factors. Most often the neuropathy is unilateral, but Ecker and Woltman found 20 percent of their patients to have bilateral symptoms.
Most of our patients with meralgia paresthetica request no treatment once they learn of its benign character. Weight loss and adjustment of restrictive clothing or correction of habitual postures that might compress the nerve are sometimes helpful. A few with the most painful symptoms have demanded a neurectomy or section of the nerve, but it is always wise to perform a lidocaine block first, so that the patient can decide whether the persistent numbness is preferable. In one specimen of nerve obtained at operation, we found a discrete traumatic neuroma. Corticosteroid injections at the point of entrapment may have helped in a few cases, but this has not been studied in a systematic way.
This nerve arises from the third and fourth and to a lesser extent the second lumbar roots. It supplies the adductors of the thigh and contributes to the innervation of the internal and external rotators. The adductors have the added function of contributing to flexing the hip. The nerve may be injured by the fetal head or forceps during the course of a difficult labor or compressed by an obturator hernia. Rarely, it is affected with diabetes, polyarteritis nodosa, and osteitis pubis and by retroperitoneal spread of carcinoma of the cervix, uterus, and other tumors (Rogers et al).