What is the diagnosis for a patient with right buttock and lateral hip pain radiating down to the lower right leg, diminished sensation to light touch along the medial aspect of the right lower leg, and slightly diminished deep tendon reflexes on the right side?

L4 Lumbar Radiculopathy

This patient has L4 lumbar radiculopathy based on the classic triad of diminished sensation along the medial lower leg (L4 dermatome), asymmetrically diminished patellar reflex (1+ right vs 3+ left), and pain radiating from the buttock down the lateral thigh into the lower leg. 1

Clinical Reasoning

Key Diagnostic Features Supporting L4 Radiculopathy

The clinical presentation demonstrates several hallmark features of L4 nerve root compression:

• Sensory deficit in L4 dermatome: Diminished light touch sensation along the medial aspect of the right lower leg just inferior to the knee is the classic L4 sensory distribution 1, 2
• Asymmetric patellar reflex: The 1+ patellar reflex on the right compared to 3+ on the left indicates L4 nerve root involvement, as the patellar reflex is mediated by the L4 nerve root 1, 2
• Pain radiation pattern: Pain radiating from buttock through lateral hip and down the leg below the knee suggests nerve root compromise, consistent with lumbar radiculopathy 1
• Neuropathic pain quality: The aching and intermittently sharp, burning character is typical of radicular pain 3, 1

Features That Exclude Alternative Diagnoses

Piriformis syndrome (Option C) is excluded because:

• Negative FABER test argues strongly against piriformis syndrome 4, 5
• Piriformis syndrome typically presents with buttock pain and tenderness in the sciatic notch, exacerbated by prolonged sitting and the FADIR maneuver (flexion, adduction, internal rotation) 4, 5, 6
• The specific L4 dermatomal sensory loss and asymmetric patellar reflex are not features of piriformis syndrome 4, 5

S1 radiculopathy (Option E) is excluded because:

• S1 radiculopathy would present with diminished or absent Achilles reflex, which is 2+ bilaterally in this patient 1, 2
• S1 sensory deficits occur along the lateral foot and posterior calf, not the medial lower leg 1, 2
• S1 motor weakness affects foot plantarflexion, not documented here 1

Greater trochanteric pain syndrome (Option A) is excluded because:

• No tenderness over the lateral hip was noted on examination 3
• This condition does not cause dermatomal sensory deficits or reflex asymmetry 3
• Pain does not typically radiate below the knee 3

Meralgia paresthetica (Option B) is excluded because:

• This involves the lateral femoral cutaneous nerve, causing numbness/burning on the anterolateral thigh only 3
• It does not cause pain radiating below the knee or reflex changes 3

Clinical Pitfalls to Avoid

Common Diagnostic Errors

• Over-reliance on straight leg raise: The negative straight leg raise in this case should not dissuade from the diagnosis of radiculopathy. While the straight leg raise has 91% sensitivity for herniated disc, it is most sensitive for L5 and S1 radiculopathies, less so for L4 1
• Ignoring subtle reflex asymmetry: The difference between 1+ and 3+ patellar reflexes is clinically significant and should not be dismissed as normal variation 2
• Confusing radiculopathy with plexopathy: True radiculopathy presents with dermatomal sensory loss and single nerve root reflex changes, whereas plexopathy would affect multiple peripheral nerve distributions 3

Important Clinical Context

Most symptomatic lumbar disc herniations occur at L4/L5 and L5/S1 levels, making L4 radiculopathy a common presentation 1. The gradual onset over two weeks without trauma is typical for degenerative disc disease causing nerve root compression 1, 2.