Differential Diagnosis for Lower Back Pain Radiating to Shin and Toes

Single Most Likely Diagnosis

• Lumbar Disc Herniation (L4-L5 or L5-S1): This condition is the most likely cause due to the symptom of pain radiating down to the shin and toes, which is consistent with sciatic nerve involvement. The inability to bend the leg without it buckling and the need to keep the leg straight to ambulate also suggest nerve root compression, commonly seen in lumbar disc herniations.

Other Likely Diagnoses

• Lumbar Spondylosis: This condition involves wear and tear on the spine, which can lead to nerve compression and similar symptoms.
• Lumbar Spinal Stenosis: Narrowing of the spinal canal can compress nerves, causing pain and weakness in the legs, especially when walking or bending.
• Piriformis Syndrome: Compression of the sciatic nerve by the piriformis muscle can cause pain that radiates down the leg, although it less commonly causes significant weakness.

Do Not Miss Diagnoses

• Cauda Equina Syndrome: A serious condition where the nerves in the spinal canal are compressed, leading to severe pain, numbness, and potentially permanent nerve damage if not promptly treated. Symptoms can include sudden loss of bladder and bowel control, which are red flags.
• Spinal Infection (e.g., Abscess or Osteomyelitis): Infections in the spine can cause severe back pain and neurological deficits. Fever, recent travel, or immune compromise could increase suspicion.
• Spinal Tumor: Both primary and metastatic tumors can compress nerves, causing pain and neurological symptoms. A history of cancer or unexplained weight loss could raise suspicion.

Rare Diagnoses

• Arachnoiditis: Inflammation of the membranes surrounding the spinal cord, which can cause severe pain and neurological symptoms.
• Tarlov Cysts: Fluid-filled sacs that can compress nerves, leading to pain and neurological deficits.
• Neurosyphilis: A complication of untreated syphilis that can cause a variety of neurological symptoms, including pain and weakness.

Each of these diagnoses has the potential to explain the symptoms described, but the likelihood and urgency of each condition vary, emphasizing the importance of a thorough medical evaluation to determine the correct diagnosis and appropriate treatment.