Lumbar Herniated Disc: This is the most common cause of low back pain with leg weakness and neuropathy, as the herniated disc can compress the nerve roots, leading to pain, weakness, and numbness in the legs.

Lumbar Spinal Stenosis: This condition involves narrowing of the spinal canal, which can compress the nerve roots and cause pain, weakness, and numbness in the legs.
Degenerative Disc Disease: Wear and tear on the spinal discs can cause pain, weakness, and numbness in the legs, especially if the discs are compressing the nerve roots.
Spondylolisthesis: A condition where a vertebra slips out of place, which can compress the nerve roots and cause pain, weakness, and numbness in the legs.

Cauda Equina Syndrome: A serious condition where the nerves in the lower spine are compressed, which can cause severe pain, weakness, and numbness in the legs, as well as bowel and bladder dysfunction. If missed, it can lead to permanent damage.
Spinal Infection (e.g., Abscess or Osteomyelitis): Infections in the spine can cause pain, weakness, and numbness in the legs, and can be life-threatening if not treated promptly.
Spinal Tumor: Tumors in the spine can compress the nerve roots and cause pain, weakness, and numbness in the legs, and can be life-threatening if not treated promptly.

Arachnoiditis: Inflammation of the membranes surrounding the spinal cord, which can cause pain, weakness, and numbness in the legs.
Tarlov Cyst: A rare condition where a cyst forms in the spine, which can compress the nerve roots and cause pain, weakness, and numbness in the legs.
Neurosyphilis: A rare condition where syphilis infects the nervous system, which can cause pain, weakness, and numbness in the legs.