Lumbosacral L5-S1 plexopathy?

60 y/o male with complaint of unilateral left lower extremity burning pain x 2 years. Starts in his buttocks and the pain goes to his knee. Pt denies any trauma, falls, weakness or atrophy. The pain is worse when he tries to elevate the left leg, standing, or bending. Pt denies any weight loss. Pt with minimum back pain. (+) shopper's cart sign. The neurontin seems to help with the pain

Physical Exam:
SLR negative both legs.
Reflexes: Absent Left achilles reflex , and 2+ Right...

Lumbosacral L5-S1 plexopathy?