What are the possible causes of chronic lower back pain and stiffness?

Causes of Chronic Lower Back Pain and Stiffness

Chronic lower back pain and stiffness can arise from mechanical disorders (osteoarthritis, spinal stenosis, disc disease), inflammatory conditions (axial spondyloarthropathies including ankylosing spondylitis), or serious underlying pathology (malignancy, infection, compression fractures), with inflammatory causes particularly important to identify in younger patients presenting with characteristic morning stiffness and pain that improves with exercise. 1, 2

Mechanical Causes

Degenerative and Structural Disorders

• Osteoarthritis and facet joint disease are common mechanical causes of chronic lower back pain, though degenerative changes on imaging correlate poorly with symptoms 3, 4
• Lumbar spinal stenosis causes neurogenic claudication characterized by leg pain and weakness with walking or standing, relieved by sitting or spinal flexion 1, 3
• Discogenic pain from intervertebral disc degeneration can produce chronic axial back pain without radicular symptoms 4, 5
• Sacroiliac joint dysfunction may contribute to chronic lower back and buttock pain 4

Myofascial Pain

• Muscle strain and myofascial pain syndrome represent common sources of chronic mechanical back pain 4, 5

Inflammatory Spondyloarthropathies

Axial Spondyloarthropathies (axSpA)

This category is critically important because it affects up to 5% of chronic back pain patients and requires early diagnosis to prevent disability. 1

• Ankylosing spondylitis is the prototypical inflammatory cause, with prevalence estimates ranging from 0.3% to 5% in primary care patients with chronic back pain 1
• Psoriatic arthritis, reactive arthritis, and inflammatory bowel disease-related spondyloarthropathies also cause axial inflammation 1

Key Clinical Features Suggesting Inflammatory Cause

• Onset before age 45 years is characteristic of axial spondyloarthropathies 1, 2
• Inflammatory back pain (IBP) features include:
  • Morning stiffness lasting >30 minutes 1, 2
  • Pain at night or early morning that awakens the patient 1
  • Pain that improves with exercise but not rest 1
  • Alternating buttock pain 1
• Sacroiliitis detected by radiography or MRI confirms inflammatory involvement 1

Diagnostic Testing for Inflammatory Causes

• HLA-B27 testing has 90% sensitivity and provides a post-test probability of 32% when positive, making it an ideal screening test for axial spondyloarthropathy 1
• ESR and CRP have only 50% sensitivity and are not suitable for screening, though elevated levels may support the diagnosis 1
• MRI of sacroiliac joints can detect pre-radiographic inflammatory changes using fluid-sensitive sequences (T2-weighted fat-saturated or STIR) 1

Serious Underlying Pathology ("Red Flags")

Malignancy

• History of cancer increases post-test probability from 0.7% to 9% (positive likelihood ratio 14.7) 2, 6
• Unexplained weight loss (likelihood ratio 2.7), failure to improve after 1 month (likelihood ratio 3.0), and age >50 years (likelihood ratio 2.7) suggest malignancy 2, 6
• Malignancy accounts for approximately 0.7% of primary care back pain cases 1

Spinal Infection

• Fever, recent infection, intravenous drug use, and immunocompromised status are key risk factors 2, 6
• Spinal infections account for only 0.01% of cases but carry high morbidity and mortality if untreated 1, 6

Compression Fractures

• Older age, history of osteoporosis, and corticosteroid use increase risk for vertebral compression fractures 2
• Compression fractures occur in approximately 4% of primary care patients with back pain 1

Cauda Equina Syndrome

• Urinary retention, fecal incontinence, saddle anesthesia, and motor deficits at multiple levels indicate this rare (0.04% prevalence) but urgent condition 1, 2, 6

Radiculopathy and Nerve Root Compression

• Symptomatic herniated disc occurs in approximately 4% of patients and causes radicular pain in a typical lumbar nerve root distribution 1, 2
• Spinal stenosis affects about 3% of patients and may cause both axial pain and neurogenic claudication 1

Non-Spinal Referred Pain

• Vascular disorders (abdominal aortic aneurysm), gynecologic conditions (endometriosis), and visceral pathology can refer pain to the lower back 5

Critical Diagnostic Pitfalls to Avoid

• Do not assume all morning stiffness is mechanical—inflammatory back pain with stiffness >30 minutes improving with exercise suggests axial spondyloarthropathy and warrants HLA-B27 testing and rheumatology referral 1
• Do not delay imaging when red flags are present—immediate MRI is indicated rather than waiting 4-6 weeks 2, 6
• Do not rely on ESR/CRP alone to screen for inflammatory causes—these have only 50% sensitivity in ankylosing spondylitis 1
• Do not overlook age of onset—symptoms beginning before age 45 significantly increase likelihood of inflammatory spondyloarthropathy 1