Differential Diagnosis for Chronic Backache with Buttock and Thigh Pain

Single Most Likely Diagnosis

• Piriformis Syndrome: This condition is characterized by pain in the buttock that radiates down the back of the thigh, which matches the patient's symptoms. The pain is often exacerbated by activities that involve running or sitting, which also aligns with the patient's experience. The specific exam findings, such as pain reduction when resisting external rotation of the hip while it is extended and internally rotated, and pain reproduction when resisting abduction and external rotation, are classic for piriformis syndrome. The piriformis muscle can compress the sciatic nerve, leading to these symptoms.

Other Likely Diagnoses

• Lumbar Disc Herniation: This condition can cause back pain that radiates down the thigh due to nerve root compression. However, the specific exam maneuvers that reproduce or alleviate pain might not as directly implicate the piriformis muscle as they do in this case.
• Sacroiliac Joint Dysfunction: Pain from sacroiliac joint dysfunction can radiate into the buttock and thigh. While the exam findings could suggest this diagnosis, the specific patterns of pain with resisted movements are more indicative of piriformis syndrome.
• Trochanteric Bursitis: Inflammation of the bursa over the greater trochanter can cause lateral hip pain, but the radiation of pain down the back of the thigh and the specific exam findings are less typical for this condition.

Do Not Miss Diagnoses

• Cauda Equina Syndrome: A serious condition that requires immediate medical attention, characterized by low back pain, bilateral sciatica, and potentially bladder and bowel dysfunction. Although the patient's symptoms do not directly suggest cauda equina syndrome, any condition causing significant neurological symptoms or bladder/bowel dysfunction must be ruled out.
• Spinal Stenosis: Can cause back and leg pain, especially with walking or standing, and is a condition that should not be missed due to its potential for significant disability.

Rare Diagnoses

• Neoplastic Processes: Tumors affecting the spine, pelvis, or soft tissues can cause back and leg pain. These are less common but must be considered, especially if there are systemic symptoms like weight loss or if the pain pattern is atypical.
• Inflammatory Spondyloarthropathies: Conditions like ankylosing spondylitis can cause chronic back pain and stiffness, but the specific pattern of pain radiation and exam findings in this case make these diagnoses less likely.