What are the differential diagnoses to consider in a patient presenting with symptoms of a slipped disc, such as back pain, numbness, tingling, or weakness in the legs?

Differential Diagnoses for Slipped Disc (Lumbar Disc Herniation)

When evaluating a patient with suspected lumbar disc herniation, you must systematically exclude spinal stenosis, hip/joint arthritis, nerve root compression from other causes, cauda equina syndrome, and vascular claudication, as these conditions frequently mimic disc herniation but require different management approaches.

Primary Differential Diagnoses

Lumbar Spinal Stenosis

• Presents with pseudoclaudication (neurogenic claudication), not pain that worsens when standing from sitting 1
• Occurs in only 3% of patients with low back pain and is more common in patients older than 65 years 1
• Symptoms typically include bilateral leg pain, numbness, or weakness that worsens with walking or standing and improves with sitting or lumbar flexion 2
• Only 61% of stenosis patients eventually develop true neurogenic claudication, making this diagnosis challenging 2
• Reduced ankle jerks are the most common examination finding, with generally mild neurological abnormalities 2

Hip Arthritis (Greater Trochanteric Pain Syndrome)

• Produces lateral hip and thigh aching discomfort that occurs after variable degrees of exercise 3
• Pain is not quickly relieved by rest and improves when not bearing weight 3
• Lacks the specific dermatomal distribution seen in true radiculopathy 4
• Does not produce positive straight-leg-raise test (which has 91% sensitivity for disc herniation) 1, 4
• Neurological examination shows no reflex, motor, or sensory deficits corresponding to specific nerve root levels 4

Nerve Root Compression from Other Causes

• Spinal stenosis with nerve root compression causes pain and weakness that may mimic claudication, with variable relief that can take a long time to recover 3
• Relief occurs with lumbar spine flexion; symptoms worsen with standing and extending the spine 3
• Often bilateral buttocks and posterior leg involvement 3

Sacroiliac Joint Dysfunction

• Can produce pseudoradicular lower back syndrome that mimics disc herniation 5
• SIJ tenderness is present in 65% of patients with L5-S1 disc herniation versus 35% with L4-5 herniation, making this a common coexisting finding rather than a separate diagnosis 5
• Restricted SIJ movement occurs in 84% of disc herniation patients 5
• Painful palpation of the symphysis demonstrated in 46% of disc herniation cases 5

Foot/Ankle Arthritis

• Produces ankle, foot, or arch aching pain after variable exercise 3
• May be present at rest and not quickly relieved 3
• May improve with non-weight bearing 3

Critical Red Flags Requiring Immediate Evaluation

Cauda Equina Syndrome

• Characterized by urinary retention, fecal incontinence, and saddle anesthesia—requires urgent MRI and surgical evaluation 1, 6
• Can occur with large central disc herniations, though rare 6
• Represents the only absolute emergency indication for immediate imaging and surgery 1

Malignancy

• Suspect in patients with history of cancer, unexplained weight loss, age over 50 years, or failure to improve after 1 month 1

Infection

• Suspect in patients with fever, IV drug use, or recent infection 1

Compression Fracture

• Suspect in older patients with osteoporosis history or steroid use 1

Vascular Causes (Less Common but Important)

Peripheral Artery Disease (PAD)

• Produces claudication with aching, burning, cramping, or fatigue in buttock, thigh, calf, or ankle 3
• Onset with distance or exercise, with relief typically within 10 minutes of rest 3
• Abnormal lower extremity pulse palpation distinguishes this from neurogenic causes 3

Venous Claudication

• Produces tight, bursting pain in entire leg, worse in calf 3
• Occurs after walking, subsides slowly, and relief is speeded by leg elevation 3
• History of iliofemoral deep vein thrombosis with edema and signs of venous stasis 3

Key Distinguishing Features of True Disc Herniation

Clinical Presentation

• More than 90% of symptomatic lumbar disc herniations occur at L4/L5 and L5/S1 levels 1, 4
• Radiculopathy follows specific nerve root distribution with corresponding neurological deficits 4
• Pain worsens with positional changes consistent with mechanical nerve root compression 1
• Present in only 4% of primary care patients with low back pain 1

Specific Nerve Root Findings

• L4 nerve root (L3-L4 disc): Depression or absence of patellar tendon reflex, radicular pain down anterior and medial thigh to knee 6
• L5 nerve root (L4-L5 disc): Great toe and foot dorsiflexion weakness, sensory loss on dorsal foot 4
• S1 nerve root (L5-S1 disc): Foot plantarflexion weakness and diminished ankle reflexes 4

Physical Examination Tests

• Straight-leg-raise test: 91% sensitivity but only 26% specificity 1
• Crossed straight-leg-raise test: 88% specificity but only 29% sensitivity 1

Common Pitfalls to Avoid

• Do not assume all leg pain radiating from the back is disc herniation—only 4% of low back pain cases are due to symptomatic disc herniation 1
• Do not confuse spinal stenosis with disc herniation—stenosis presents with pseudoclaudication that improves with sitting, while disc herniation pain worsens when standing from sitting 1
• Do not overlook coexisting SIJ dysfunction—84% of disc herniation patients have restricted SIJ movement, which can confound the clinical picture 5
• Do not order immediate MRI unless red flags are present or symptoms persist beyond 4-6 weeks—most disc herniations resolve with conservative therapy 1, 7