What are the potential causes and treatment options for low back pain radiating to the left lower abdomen/pelvis?

Low Back Pain Radiating to Left Lower Abdomen/Pelvis

The most critical first step is to determine whether this represents referred visceral pain from an intra-abdominal process (particularly diverticulitis in older adults) versus musculoskeletal low back pain with atypical radiation, as these require fundamentally different diagnostic and treatment pathways.

Immediate Diagnostic Approach

Red Flag Assessment

Evaluate immediately for features requiring urgent imaging or intervention:

• Progressive motor weakness or sensory deficits in the lower extremities indicate possible nerve root compression requiring urgent MRI 1, 2
• Saddle anesthesia, bowel/bladder dysfunction, or bilateral leg weakness suggest cauda equina syndrome requiring emergent MRI and surgical consultation 2
• Fever, leukocytosis, and left lower quadrant tenderness suggest acute diverticulitis requiring CT imaging 3
• History of cancer warrants urgent MRI to exclude vertebral metastasis 1

Key Clinical Discriminators

The pattern and associated symptoms distinguish the etiology:

For Intra-abdominal/Pelvic Pathology:

• Left lower quadrant pain with fever and leukocytosis (present in only 25% of diverticulitis cases) strongly suggests sigmoid diverticulitis 3
• Pain that worsens with eating, associated with nausea, or changes with position may indicate visceral referred pain 4
• Age >45 years significantly increases likelihood of diverticulitis as 5-10% have diverticulosis by age 45, rising to 80% by age 80 3

For Musculoskeletal/Neurologic Pathology:

• Pain that worsens with spinal movement, improves with rest, or has dermatomal radiation suggests mechanical low back pain 5
• Electric-like sensations radiating down the leg indicate radiculopathy requiring different management 1

Imaging Strategy

When Diverticulitis is Suspected (Older Adult, Left Lower Quadrant Pain)

CT abdomen/pelvis with IV contrast is the imaging examination of choice with 98% accuracy for diagnosing diverticulitis and its complications 3:

• Demonstrates bowel wall thickening, pericolonic fat stranding, abscesses, fistulas, and perforation 3
• Low-dose CT techniques can reduce radiation by 75-90% without compromising diagnostic accuracy 3
• Oral or rectal contrast may be helpful but is not mandatory 3
• Imaging may be omitted only in patients with typical recurrent symptoms and prior documented diverticulitis without suspected complications 3

When Neurologic Deficits are Present

Urgent MRI of the lumbar spine is mandatory when motor weakness, progressive sensory loss, or severe radicular symptoms are present 1, 2:

• MRI provides superior visualization of nerve roots, spinal canal, and intervertebral discs 2
• Do NOT delay imaging for a trial of conservative therapy when neurologic deficits exist 2
• Plain radiographs are inadequate as they cannot visualize discs or nerve roots 2

When Neither Clear Pattern Exists

• Plain radiography has extremely limited utility for initial evaluation of this presentation 3
• Consider CT abdomen/pelvis first if patient is >45 years old, as visceral pathology is more likely to cause serious morbidity if missed 3

Treatment Based on Diagnosis

For Confirmed Diverticulitis

• Mild uncomplicated cases: Outpatient management with oral antibiotics and bowel rest 3
• Complicated cases with abscess: May require percutaneous drainage or surgery 3
• Recurrent diverticulitis or fistula formation: Surgical consultation for elective sigmoidectomy 3

For Mechanical Low Back Pain Without Red Flags

Acute Phase (<4 weeks):

• NSAIDs provide moderate evidence of benefit for short-term pain relief 3, 5
• Spinal manipulation shows small to moderate short-term benefits when administered by appropriately trained providers 3
• Advise patients to stay active and avoid bed rest (level Ia evidence) 6
• Acetaminophen has little to no evidence of benefit for low back pain 5

Chronic Phase (>12 weeks):

• Exercise therapy with individual tailoring, supervision, stretching, and strengthening shows best outcomes 3
• Yoga (Viniyoga-style) has strong evidence for long-term effectiveness 3, 5
• Acupuncture, massage therapy, and cognitive-behavioral therapy show moderate effectiveness 3
• Duloxetine is the only antidepressant with evidence of benefit; other antidepressants lack supporting evidence 5

For Radiculopathy With Motor Deficits

• Urgent neurosurgical consultation if progressive weakness or cauda equina features present 2
• Large disc herniation with nerve root compression may require surgical decompression 2

Critical Pitfalls to Avoid

1. Do not assume all low back pain is musculoskeletal - visceral pathology (diverticulitis, duodenal ulcer, gynecologic disease) can present as back pain 4
2. Do not order plain radiographs as initial imaging when neurologic deficits are present 2
3. Do not delay imaging in patients with motor weakness - the standard recommendation against routine imaging does not apply when neurologic deficits exist 2
4. Do not miss diverticulitis in older adults - the classic triad of fever, leukocytosis, and left lower quadrant pain is present in only 25% of cases 3
5. Do not use MRI as initial test for suspected diverticulitis - CT is faster, more available, and equally accurate 3