What are the differences between lumbar degenerative joint disease, lumbar radiculopathy, and lumbar myelopathy?

Distinguishing Lumbar Degenerative Joint Disease, Radiculopathy, and Myelopathy

Lumbar degenerative joint disease (DJD) causes axial back pain from structural degeneration; radiculopathy produces nerve root dysfunction with dermatomal pain and neurological deficits; and true myelopathy does not occur in the lumbar spine because the spinal cord ends at L1-L2, making "lumbar myelopathy" a misnomer—what clinicians may call lumbar myelopathy is actually cauda equina syndrome.

Lumbar Degenerative Joint Disease (DJD)

Core Pathophysiology

• DJD represents structural degeneration of the three-joint complex (one intervertebral disc and two facet joints) at each spinal level, progressing through mechanical stress, inflammatory changes, and eventual multilevel involvement 1, 2.
• Degeneration starts in one joint and eventually involves all three joints of the three-joint-complex, later affecting levels above and below through mechanical changes 3.
• DJD is a pathologic process influenced by mechanical stress and inflammation, not simply normal aging 2.

Clinical Presentation

• Primary symptom is axial low back pain localized to the lumbar region without radiation below the knee 1.
• Pain is mechanical in nature—worsens with activity, improves with rest 4.
• No dermatomal radiation, no neurological deficits (weakness, sensory loss, reflex changes) unless neural compression develops 1.
• Degenerative changes on imaging correlate poorly with symptoms—many asymptomatic individuals have significant radiographic degeneration 1.

Imaging Features

• MRI demonstrates disc degeneration, facet joint arthropathy, endplate changes (Modic changes), and osteophyte formation 2, 5.
• Modic type 1 changes indicate active vertebral inflammation and are specific predictors of concordant pain 1, 5.

Lumbar Radiculopathy

Core Pathophysiology

• Radiculopathy is dysfunction of a nerve root associated with pain, sensory impairment, weakness, or diminished deep tendon reflexes in a nerve root distribution 1.
• Caused by mechanical compression or inflammation of nerve roots from disc herniation, foraminal stenosis, or osteophytes 1, 5.
• More than 90% of symptomatic lumbar disc herniations occur at L4/L5 and L5/S1 levels 6.

Clinical Presentation

• Sciatica is the hallmark—pain radiating down the leg below the knee in sciatic nerve distribution 1, 6.
• Dermatomal sensory deficits: L4 (medial leg/foot), L5 (lateral leg/dorsal foot), S1 (lateral foot/heel) 6.
• Motor weakness in specific patterns: L4 (knee extension/patellar reflex), L5 (great toe/foot dorsiflexion), S1 (foot plantarflexion/ankle reflex) 6.
• Positive straight-leg raise test (30-70 degrees) has 91% sensitivity for herniated disc; crossed straight-leg raise is more specific (88%) but less sensitive (29%) 6.

Diagnostic Algorithm

• Clinical diagnosis based on dermatomal pain pattern plus corresponding neurological deficits 1, 6.
• MRI is NOT indicated initially—only order if patient is surgical candidate or symptoms persist beyond 4 weeks of conservative management 6.
• Imaging findings must correlate with clinical symptoms to avoid unnecessary intervention 6, 5.

Management Pathway

• Conservative management for minimum 6 months unless red flags present: physical therapy, activity modification, neuropathic pain medications (gabapentin, pregabalin) 4, 6.
• Surgical indications: cauda equina syndrome, progressive neurological deficits, or severe disabling pain refractory to 6 months conservative therapy 6.
• Simple discectomy without fusion is appropriate for isolated radiculopathy without chronic axial pain or instability 6.

"Lumbar Myelopathy" vs. Cauda Equina Syndrome

Critical Anatomical Distinction

• The spinal cord terminates at L1-L2 level—below this are only nerve roots (cauda equina), not spinal cord 1.
• True myelopathy cannot occur in the lumbar spine because there is no spinal cord to compress at lumbar levels.
• What clinicians may incorrectly term "lumbar myelopathy" is actually cauda equina syndrome—compression of multiple nerve roots from lower cord segments 1.

Cauda Equina Syndrome Presentation

• Urinary retention or incontinence from loss of sphincter function (90% sensitivity for cauda equina) 1, 6.
• Bilateral motor weakness of lower extremities 1.
• Saddle anesthesia—sensory loss in perineal/perianal region 1.
• Bowel incontinence may occur 6.

Emergency Management

• Cauda equina syndrome requires emergency surgical decompression—delays result in permanent neurological damage 6.
• Immediate MRI and urgent surgical consultation are mandatory 6.

Differentiating the Three Conditions

Pain Pattern

• DJD: Axial back pain only, no leg radiation 1.
• Radiculopathy: Dermatomal leg pain below knee, may have back pain 1, 6.
• Cauda equina: Bilateral leg symptoms, perineal numbness, sphincter dysfunction 1, 6.

Neurological Examination

• DJD: Normal motor, sensory, and reflex examination 1.
• Radiculopathy: Unilateral dermatomal sensory loss, specific motor weakness, diminished reflex in nerve root distribution 1, 6.
• Cauda equina: Bilateral motor weakness, saddle anesthesia, absent ankle reflexes bilaterally 1, 6.

Imaging Correlation

• DJD: Degenerative changes without neural compression; imaging findings often do not correlate with symptoms 1, 2.
• Radiculopathy: Nerve root compression (disc herniation, foraminal stenosis) at level corresponding to clinical symptoms 1, 5.
• Cauda equina: Massive central disc herniation or severe central canal stenosis compressing multiple nerve roots 1.

Common Pitfalls to Avoid

• Do not equate radiographic degeneration with clinical significance—degenerative changes are common in asymptomatic individuals and correlate poorly with symptoms 1.
• Do not order MRI for acute radiculopathy—imaging is only indicated if patient is surgical candidate or symptoms persist beyond 4 weeks 6.
• Do not delay surgical consultation for suspected cauda equina syndrome—urinary retention has 90% sensitivity and requires emergency intervention 6.
• Do not use the term "lumbar myelopathy"—the spinal cord ends at L1-L2; compression below this level affects nerve roots (cauda equina), not spinal cord 1.
• Do not perform fusion for isolated radiculopathy—simple discectomy is sufficient unless chronic axial pain or instability present 6.