A Woman With Back Pain and Leg Weakness

A 45-year-old woman without significant past medical history developed numbness in the inner aspect of the left leg and nonradiating back pain. She also had left leg weakness and locking with instability resulting in a fall, causing a fracture of the left second toe 3 weeks prior to her evaluation.

Neurologic examination revealed normal mentation and cranial nerves. Motor and sensory examinations were normal in both upper extremities and right leg. In the left lower extremity the left quadriceps muscle was weak at 4+/5 and the adductors were 5−/5. All reflexes were 2+ (normal), except in the left patellar and left adductor reflexes that were 1+. There was a patchy area of decreased sensation in the anterior left thigh. Straight leg raising and femoral stretch ¹ tests were normal. The rest of the neurologic examination was unremarkable.

What is the Differential Diagnosis?

This healthy woman had back pain and weakness limited to muscles innervated by L3–L4. ² She appeared to have a lumbosacral radiculopathy most likely caused by a disk herniation. A lumbosacral radiculoplexopathy from diabetes is unlikely as she is not diabetic; there are, however, instances of nondiabetic idiopathic or autoimmune lumbosacral plexopathy. ³ Lumbosacral radiculoplexopathy could also be caused by herpes zoster and CMV infection in HIV-positive individuals. ^4–6 Other possibilities include tumors, abscesses, and hematomas of the retroperitoneal space and pelvis causing a plexopathy. The weak adductors and decreased adductor reflex argue against a femoral neuropathy. ( Table 18-1 outlines the neurologic findings in the various lumbosacral radiculopathies; Table 18-2 outlines their differential diagnosis.)

Table 18-1

Neurologic Findings in Lumbosacral Monoradiculopathies

From Raynor EM, Kleiner-Fisman G, Nardin R. Lumbosacral and thoracic radiculopathies. In: Katirji B, Kaminski HJ, Preston DC, et al., eds. Neuromuscular Disorders in Clinical Practice . Boston, MA: Butterworth-Heinemann; 2002:864.

Root Level	Pain	Sensory Loss (Paresthesias)	Motor Abnormalities/Weakness	Deep Tendon Reflex Abnormalities
L1	Inguinal region	Inguinal region	None	None
L2	Groin, anterior thigh	Anterolateral thigh	Iliopsoas	None
L3	Anterior thigh to knee	Medial thigh and knee	Quadriceps, iliopsoas, and hip adductors	Knee jerk
L4	Anterior thigh to medial foreleg	Medial leg	Tibialis anterior, quadriceps, and hip adductors	Knee jerk
L5	Lateral thigh and leg to dorsum foot	Lateral leg, dorsum foot, and great toe	Toe extensors, ankle dorsiflexors, evertor and invertors, and hip abductors	None (unless S1 involved)
S1	Posterior thigh, calf, and heel	Sole, lateral foot and ankle, and lateral two toes	Toe flexors, gastrocnemii, hamstrings, and gluteus maximus	Ankle jerk
S2–S4	Medial buttocks	Medial buttocks, perineal and perianal region	None unless S1 through S2 involved	Bulbocavernosus and anal wink (ankle jerk if S1 involved)

Table 18-2

Differential Diagnosis of Lumbosacral Monoradiculopathies

Root Level	Nerve Lesion	Plexus Lesion	Differential Features
L1	Ilioinguinal neuropathy; genitofemoral neuropathy	Unlikely	Sensory loss outside single nerve territory
L2	Lateral femoral cutaneous neuropathy (meralgia paresthetica)	High lumbar plexopathy	Strength normal in meralgia paresthetica; quadriceps more involved with femoral neuropathy
L3	Femoral neuropathy	High lumbar plexopathy; diabetic amyotrophy	Adductor weakness not seen with femoral neuropathy
L4	Femoral neuropathy	Mid lumbar plexopathy	Tibialis anterior, hip adductors not involved in femoral neuropathy; quadriceps not involved in peroneal neuropathy
L5	Common peroneal neuropathy	Mid lumbar plexopathy	Ankle inversion not involved in peroneal neuropathy; hip abduction also normal with peroneal neuropathy
S1	Sciatic neuropathy	Lower lumbosacral plexopathy	Hamstrings not involved in tibial neuropathy; glutei not involved in sciatic neuropathy

What should be the Diagnostic Workup?

The patient had a normal comprehensive metabolic panel and glycosylated hemoglobin and erythrocyte sedimentation rate.

An EMG Test was Performed

Motor Nerve Studies

Nerve and Site	Latency(ms)	Amplitude (mV)	Conduction Velocity (m/s)
Peroneal Nerve L.	Normal ≤ 5.3	Normal ≥ 3	Normal ≥ 40
Ankle	3.7	3	–
Fibular head	11.9	2	45
Knee	13.4	2	66

Tibial Nerve L.	Normal ≤ 5.3	Normal ≥ 4	Normal ≥ 40
Ankle	3.5	19	–
Pop. fossa	13.4	12	43

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Peroneal Nerve R.	Normal ≤ 5.7	Normal ≥ 3	Normal ≥ 40
Ankle	4.9	5	–
Fibular head	11.2	4	46
Knee	12.8	4	56

F-Wave Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Peroneal nerve L.	50.4	54
Tibial nerve L.	50.2	54
Peroneal nerve R.	49.0	54
H-reflex L.	33.9	34
H-reflex R.	33.8	34

Sensory Nerve Studies

Nerve	Onset Latency (ms)	Normal Onset Latency ≤ (ms)	Peak Latency (ms)	Normal Peak Latency ≤ (ms)	Amp (μV)	Normal Amp ≥ (mV)	Conduction Velocity (m/s)	Normal Conduction Velocity ≥ (m/s)
Sural nerve L.	3.0	3.5	3.5	4.0	7	11	47	40
Superficial peroneal L.	NR	3.5	NR	4.0	NR	10	NR	40
Sural nerve R.	3.2	3.5	3.7	4.0	12	11	44	40
Superficial peroneal R.	3.4	3.5	3.9	4.0	9	8–10	41	40