Lba and Lower abd pain d/ds

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Differential Diagnoses: Low Back Pain (LBP) & Lower Abdominal Pain

LOW BACK PAIN — Differential Diagnoses

Classification Framework (Harrison's, 22e)

LBP is categorized by pain type, which guides the differential:

Pain Type	Characteristics	Common Causes
Nociceptive	Worsens with activity, progressive, localizable	Musculoskeletal, degenerative
Neuropathic	Paresthesias, numbness, allodynia, dermatomal	Radiculopathy, spinal stenosis
Nociplastic	Diffuse, superficial, non-dermatomal, central sensitization	Fibromyalgia, non-specific LBP

I. MUSCULOSKELETAL (Most Common)

A. Myofascial / Muscle Strain (~70% of acute LBP)

Focal or diffuse paraspinal tenderness, limited ROM
Normal neurology; may have trigger points
Often precipitated by lifting, twisting, overexertion

B. Discogenic Pain (26–42% of axial LBP)

Worse with sitting and forward flexion
Often bilateral, non-dermatomal radiation to legs
Disk degeneration → annular tears → inflammatory cytokines

C. Facet Joint Pain (~10–15%)

Worse with extension, standing, walking
Paraspinal tenderness; radiation to buttock/thigh (not below knee)
Increases with age (degeneration)

D. Sacroiliac (SI) Joint Pain

Pain below L5, radiation into groin
≥3 positive provocation tests (Patrick's, Gaenslen's, compression, distraction)
Common postpartum or with spondyloarthropathy

E. Spondylolisthesis

Forward slip of vertebral body; decreased extension ROM
May cause canal stenosis with myelopathy or radiculopathy

F. Spondylolysis (Stress fracture of pars interarticularis)

Common in athletes doing hyperextension sports (gymnastics, football)
Most common cause of LBP in adolescent athletes
Textbook of Family Medicine 9e, p. 794

G. Spinal Stenosis

Neurogenic claudication: leg pain worse with walking/standing, relieved by sitting or flexion
Positive treadmill test, perineal numbness → high predictive value
Older adults; bilateral symptoms

H. Lumbar Disk Herniation with Radiculopathy

Positive SLR (30–70°) = high sensitivity for L5–S2 root
Crossed SLR = >85% specific
Femoral stretch test for mid-lumbar roots (L2–L4)
Common: L4–L5, L5–S1 levels

II. INFLAMMATORY / AUTOIMMUNE

Ankylosing Spondylitis / Axial Spondyloarthropathy

Young males, insidious onset, age <45
Morning stiffness >1 hour, improves with exercise, night pain
Elevated ESR/CRP, HLA-B27 positive
Sacroiliitis on MRI/X-ray

Psoriatic Arthritis, Reactive Arthritis, IBD-associated arthropathy

Axial involvement with inflammatory back pain features

Rheumatoid Arthritis

Cervical > lumbar; can cause atlantoaxial instability

III. INFECTIOUS

Condition	Key Features
Vertebral osteomyelitis	Fever, tenderness, elevated inflammatory markers; IV drug use, immunosuppression
Epidural abscess	Fever + severe back pain + neurologic deficit = emergency
Discitis	More common in children; elevated ESR/CRP
Herpes zoster	Dermatomal pain before rash; vesicular eruption
Psoas abscess	Referred to hip/thigh, fever, hip flexion

Red flag: Fever + back pain + palpation tenderness → imaging (MRI) mandatory — Bradley & Daroff's Neurology, p. 796

IV. NEOPLASTIC

Condition	Key Features
Metastatic disease	Most common spinal tumor (lung, breast, prostate, kidney, thyroid)
Multiple myeloma	Punched-out lytic lesions, hypercalcemia, Bence-Jones protein
Primary spinal tumors	Meningioma, ependymoma, schwannoma
Cauda equina syndrome	Saddle anesthesia, urinary/bowel incontinence — surgical emergency

Red flag: Pain worse in recumbent position, weight loss, history of cancer → imaging mandatory

V. REFERRED / VISCERAL PAIN — LBP Mimics

These are critical not to miss:

Source	Condition
Aortic	Abdominal aortic aneurysm (AAA) — tearing pain, pulsatile mass
Renal	Nephrolithiasis, pyelonephritis, hydronephrosis
Retroperitoneal	Retroperitoneal hematoma, lymphoma
Gynecologic	Endometriosis, PID, ectopic pregnancy, ovarian cyst
GI	Pancreatitis (can radiate to back), colon cancer
Vascular	Renal artery stenosis, aortic dissection
Prostate	Prostatitis, prostate cancer

VI. METABOLIC / ENDOCRINE

Osteoporosis with compression fracture: Sudden-onset pain, older women, post-menopausal, steroid use
Paget's disease of bone: Elevated ALP, bone expansion
Hyperparathyroidism: Bone pain, hypercalcemia
Fluorosis (endemic areas)

VII. PSYCHOSOCIAL / FUNCTIONAL

Nonspecific / nociplastic LBP: Chronic, diffuse, no structural correlate
Somatoform/somatic symptom disorder
Fibromyalgia: Multiple tender points, fatigue, sleep disturbance
Conversion disorder / functional neurological disorder
Co-prevalence of depression: 33–67%; anxiety: 10–30% in chronic LBP (Harrison's 22e, p. 169)

LOWER ABDOMINAL PAIN — Differential Diagnoses

(Yamada's Gastroenterology 7e; Tintinalli's Emergency Medicine; Roberts & Hedges' Clinical Procedures)

BY SYSTEM

GASTROINTESTINAL

Condition	Key Features
Appendicitis	RLQ, Rovsing's, McBurney's point, fever, raised WBC
Diverticulitis	LLQ (sigmoid), older patients, fever
Irritable Bowel Syndrome (IBS)	Chronic, relieved by defecation, altered bowel habits
Inflammatory Bowel Disease	Crohn's (RLQ, terminal ileum) / UC (diffuse, bloody diarrhea)
Colorectal cancer	Change in bowel habit, weight loss, occult bleeding
Intestinal obstruction	Colicky pain, distension, vomiting, obstipation
Inguinal / femoral hernia	Groin lump, reducible or irreducible; strangulation = emergency
Mesenteric ischemia	"Pain out of proportion", elderly, atrial fibrillation
Epiploic appendagitis	Mimic of diverticulitis/appendicitis; oval fatty mass on CT; self-limiting

UROLOGICAL

Condition	Key Features
Urinary tract infection (Cystitis)	Dysuria, frequency, urgency; suprapubic pain
Pyelonephritis	Flank pain + fever + CVA tenderness; upper UTI
Nephrolithiasis	Colicky, radiates groin, hematuria
Urinary retention	Suprapubic fullness, inability to void; BPH or neurogenic

GYNECOLOGIC (Female)

Condition	Key Features
Pelvic Inflammatory Disease (PID) / Salpingitis	Cervical motion tenderness, bilateral adnexal, vaginal discharge
Ectopic pregnancy	Sudden severe pain, missed period, positive β-hCG, shock
Ruptured ovarian cyst	Sudden onset, may have rebound tenderness
Adnexal/Ovarian Torsion	Severe unilateral colicky pain, nausea/vomiting, absent Doppler flow
Endometriosis	Dysmenorrhea, dyspareunia, cyclical pain, infertility
Tubo-ovarian Abscess	Fever, adnexal mass, severe PID
Uterine fibroids (degenerating)	Chronic or acute pain, heavy menses
Ovarian cancer	Vague pelvic discomfort, bloating, weight loss
Mittelschmerz	Mid-cycle ovulatory pain, unilateral

(Tintinalli's Emergency Medicine, p. 2086–2102)

MALE GENITAL

Condition	Key Features
Testicular torsion	Acute severe scrotal/inguinal pain, absent cremasteric reflex → surgical emergency
Epididymitis/Orchitis	Gradual onset, fever, Prehn's sign positive
Prostatitis	Perineal/suprapubic pain, dysuria, fever (acute bacterial)

VASCULAR

Abdominal aortic aneurysm (AAA): Lower abdominal + back pain, pulsatile mass — life-threatening
Iliac artery aneurysm
Mesenteric ischemia

OBSTETRIC

Threatened/inevitable abortion
Placental abruption
Round ligament pain (pregnancy)
Preterm labor

ABDOMINAL WALL

Abdominal cutaneous nerve entrapment: Very focal, worsened by tensing abdomen (Carnett's test positive)
Rectus sheath hematoma: Post-trauma or anticoagulation; tender mass, Fothergill's sign

SYSTEMIC / METABOLIC (Diffuse, Uncommon)

(Yamada's Gastroenterology 7e, p. 681)

Abdominal aortic aneurysm
Acute intermittent porphyria (colicky pain + neuropsychiatric symptoms + dark urine)
Hypercalcemia
Hypothyroidism
Lead poisoning
Hereditary angioedema (no urticaria, abdominal attacks)
Familial Mediterranean fever (recurrent episodic peritonitis)
Adult Still's disease

RED FLAGS — Require Urgent Workup

Red Flag	Suspected Diagnosis
Fever + back pain + neurologic deficit	Epidural abscess
Pain worse supine / at night	Malignancy
Saddle anesthesia + urinary/bowel incontinence	Cauda equina syndrome (EMERGENCY)
Pulsatile abdominal mass	AAA
Positive β-hCG + acute pelvic pain	Ectopic pregnancy
Absent cremasteric reflex + acute scrotal/groin pain	Testicular torsion
Severe pain + peritoneal signs	Perforation, mesenteric ischemia
Post-menopausal bleeding + pelvic pain	Endometrial/ovarian cancer
Weight loss + change in bowel habit	Colorectal cancer

Key References

Harrison's Principles of Internal Medicine 22e, Chapter 18 — Low Back Pain, pp. 161–170
Bradley & Daroff's Neurology in Clinical Practice, pp. 796–798
Yamada's Textbook of Gastroenterology 7e, p. 681
Tintinalli's Emergency Medicine, Table 71-6, pp. 2086–2102
Textbook of Family Medicine 9e, p. 794

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