What is the most likely diagnosis for a patient with a nagging backache, pain in the right buttock extending down the back of the right thigh, worsened by sitting and running, with pain reproduced by resisting external rotation and abduction?

Piriformis Syndrome

The most likely diagnosis is piriformis syndrome, a nondiscogenic cause of sciatica resulting from compression of the sciatic nerve by the piriformis muscle. 1

Clinical Presentation

The patient's presentation is classic for piriformis syndrome with the following key features:

• Buttock pain with radiation down the posterior thigh - characteristic of sciatic nerve compression by the piriformis muscle 1, 2
• Pain worsened by sitting - a hallmark symptom that distinguishes this from lumbar radiculopathy 1, 3
• Pain with running - activities that engage the piriformis muscle typically exacerbate symptoms 1

Diagnostic Physical Examination Findings

The physical examination findings are pathognomonic for piriformis syndrome:

• Pain reproduced with resisted external rotation while hip is extended and internally rotated - this is Pace's maneuver, which causes contraction of the piriformis muscle and reproduces symptoms 4, 5
• Pain reproduced with resisted abduction and external rotation while seated - another variant of testing piriformis muscle contraction that elicits deep buttock pain 4

These maneuvers rely on contraction of the piriformis muscle rather than stretching, which better reproduces the actual syndrome 4. The described examination is consistent with both Pace's sign and Beatty's maneuver, both of which are specific for piriformis syndrome 5.

Distinguishing from Other Conditions

While the American College of Physicians guidelines classify most low back pain as nonspecific 6, this patient has specific provocative maneuvers that localize pathology to the piriformis muscle rather than lumbar spine pathology.

Key differentiating features from lumbar radiculopathy:

• Patients with piriformis syndrome typically have normal neurological examination results and negative straight leg raising test results 1
• The straight-leg raise test (positive between 30-70 degrees) has 91% sensitivity for herniated disc 6, and its absence here argues against lumbar radiculopathy
• Pain reproduction with specific hip maneuvers (rather than lumbar spine movements) localizes the problem to the deep gluteal space 5

Prevalence context:

• Piriformis syndrome accounts for approximately 5-6% of all cases of low back, buttock, and leg pain, and up to 17% of patients with chronic low back pain 3
• This is more common than the 3-4% prevalence of symptomatic herniated disc or spinal stenosis in primary care 6

Diagnostic Approach

The diagnosis is clinical and one of exclusion 2, 3:

• Imaging and neurodiagnostic studies are typically normal and serve primarily to rule out other etiologies for sciatica 1
• The specific provocative maneuvers described (resisted external rotation with hip extension/internal rotation, and resisted abduction/external rotation while seated) are the cornerstone of diagnosis 4, 5
• Additional supportive findings include external tenderness over the greater sciatic notch 3

Common Pitfalls

Avoid misdiagnosing as lumbar radiculopathy:

• The absence of positive straight leg raise and normal neurological examination should redirect attention away from lumbar spine pathology 1
• Pain worsened by sitting is more consistent with piriformis syndrome than lumbar stenosis, which is typically relieved by sitting 6

Anatomic variation is not diagnostic:

• While the sciatic nerve may pierce the piriformis muscle in about 16% of healthy individuals, this frequency is no different in those with the syndrome 3