Degenerative Disc Disease: This condition is common in individuals over 50 and can cause back pain, stiffness, and exacerbation of symptoms with activities such as walking, bending, and standing up. The pain is typically localized to the lower back, which corresponds to the L3-L5 paraspinal area.

Lumbar Spondylosis: This condition involves wear and tear on the spine, leading to pain and stiffness, especially in the lower back. It can be exacerbated by activities that put strain on the spine.
Ligament Sprain or Muscle Strain: Overuse or acute injury to the muscles or ligaments in the lower back can cause pain and stiffness, particularly in the L3-L5 area.
Osteoarthritis of the Facet Joints: Inflammation and wear of the facet joints in the spine can lead to back pain, especially with movements that involve twisting or bending.

Cauda Equina Syndrome: A serious condition where the nerves in the spinal canal are compressed, leading to severe back pain, numbness, and potentially permanent nerve damage if not promptly treated.
Spinal Infection (e.g., Osteomyelitis, Discitis): Infections of the spine can cause severe back pain, fever, and other systemic symptoms. Early diagnosis and treatment are crucial to prevent serious complications.
Spinal Tumor: Although rare, tumors in the spine can cause back pain, and it's critical to rule out this possibility, especially if there are red flags such as unexplained weight loss or a history of cancer.

Ankylosing Spondylitis: A form of arthritis that primarily affects the spine, leading to chronic pain and stiffness. It's less common and typically starts at a younger age but can still be considered in the differential diagnosis.
Spondylolisthesis: A condition where one of the vertebrae slips out of place, which can cause lower back pain and stiffness. It's less common in adults without a history of trauma or congenital condition.