What is the likely cause of lower leg pain with diminished sensation along the medial aspect of the leg and limited lower back flexion?

L4 Lumbar Radiculopathy

The most likely diagnosis is L4 lumbar radiculopathy (option D), based on the characteristic medial lower leg sensory loss and asymmetric patellar reflexes, which are classic findings for L4 nerve root compression.

Clinical Reasoning for L4 Radiculopathy

The clinical presentation strongly points to L4 nerve root involvement based on several key findings:

• Diminished sensation along the medial aspect of the right lower leg just inferior to the knee is the hallmark sensory distribution of the L4 dermatome 1, 2
• Asymmetric patellar reflexes (2+ right vs 3+ left) indicate L4 nerve root dysfunction, as the knee reflex is mediated by the L4 nerve root 1, 2
• Pain radiating down the lateral thigh into the lower right leg follows a typical lumbar nerve root distribution pattern consistent with radiculopathy 1, 3
• Limited lumbar flexion due to pain suggests mechanical nerve root compression from disc herniation 3

More than 90% of symptomatic lumbar disc herniations occur at L4/L5 and L5/S1 levels, making L4 radiculopathy from L4-L5 disc herniation highly probable 1, 3.

Why Other Diagnoses Are Less Likely

Greater trochanteric pain syndrome (Option A):

• Would present with tenderness over the lateral hip, which is explicitly absent in this patient 3
• Does not cause dermatomal sensory loss or reflex asymmetry 2

Meralgia paresthetica (Option B):

• Affects the lateral femoral cutaneous nerve, causing sensory symptoms on the lateral thigh only, not extending below the knee 2
• Does not affect reflexes or cause medial lower leg sensory changes 2

Piriformis syndrome (Option C):

• Negative FABER and FADIR tests make hip pathology unlikely 3
• Would not explain the specific L4 dermatomal sensory loss or patellar reflex asymmetry 2

S1 lumbar radiculopathy (Option E):

• Would present with diminished or absent Achilles reflexes, which are normal (2+ bilaterally) in this patient 1, 2
• S1 sensory loss affects the lateral foot and posterior calf, not the medial lower leg 1, 2
• S1 radiculopathy typically causes weakness in foot plantarflexion, not present here 1

Diagnostic Approach

A focused neurological examination should assess:

• Knee strength and reflexes for L4 nerve root function 1, 3
• Great toe and foot dorsiflexion strength for L5 nerve root function 1, 3
• Foot plantarflexion and ankle reflexes for S1 nerve root function 1, 3
• Distribution of sensory symptoms in dermatomal patterns 1, 2

The straight-leg-raise test has 91% sensitivity for herniated disc, though the negative result here does not exclude L4 radiculopathy, as this test is more sensitive for lower lumbar (L5-S1) pathology 1, 3.

Management Considerations

Conservative management is appropriate initially:

• NSAIDs provide moderate pain relief for acute radicular pain 3
• Most patients improve within the first 4 weeks with noninvasive management 3
• Consider adding skeletal muscle relaxants for short-term effectiveness 3

MRI lumbar spine without contrast is indicated if:

• Symptoms persist for at least 6 weeks despite conservative management 1, 3
• There are progressive neurological deficits 1, 3
• Diagnostic uncertainty remains after clinical evaluation 1

Red flags requiring immediate imaging:

• Bowel or bladder incontinence (cauda equina syndrome) - absent in this patient 1
• Progressive motor weakness 3
• History of cancer, fever, or unexplained weight loss 1

Common Pitfalls to Avoid

• Do not confuse lateral hip pain with radiculopathy; true radiculopathy follows dermatomal patterns with objective neurological findings 1, 2
• Negative straight-leg-raise does not exclude radiculopathy, particularly at higher lumbar levels (L3-L4) 1, 4
• Asymmetric reflexes are more specific than sensory findings alone for localizing nerve root pathology 2