What is the differential diagnosis for a patient presenting with severe back pain and vomiting?

Differential Diagnosis for Severe Back Pain and Vomiting

The combination of severe back pain and vomiting requires immediate evaluation for life-threatening emergencies including vertebral osteomyelitis, cauda equina syndrome, aortic dissection, and ruptured abdominal aortic aneurysm, as these conditions can present with this symptom complex and require urgent intervention. 1, 2

Critical Red Flag Conditions to Rule Out Immediately

Spinal Emergencies

• Cauda equina syndrome presents with urinary retention (90% sensitivity), saddle anesthesia, fecal incontinence, and motor deficits at multiple levels 3, 1
• Vertebral osteomyelitis is frequently missed because fever is present in only up to 45% of cases, and the average time to diagnosis is 2-4 months due to insidious presentation 3
• Perform careful percussion of the spine to assess for vertebral osteomyelitis 3
• Obtain two sets of blood cultures and baseline ESR/CRP if vertebral osteomyelitis is suspected 3

Vascular Emergencies

• Aortic dissection and rupturing abdominal aortic aneurysm can present with severe back pain and vomiting and are immediately life-threatening 2
• These require urgent vascular imaging and surgical consultation 2

Spinal Epidural Abscess

• Spinal epidural abscess (SEA) accounts for only 0.01% of back pain cases but has high morbidity and mortality if not promptly treated 1, 2
• Risk factors include recent infection, intravenous drug use, and immunocompromised status 1

Additional Differential Diagnoses

Gastrointestinal Causes

• Acute pancreatitis classically presents with severe back pain radiating from the epigastrium and vomiting 4, 5
• Gastric outlet obstruction from malignancy can cause vomiting with referred back pain 6
• Gastroenteritis or other viral syndromes typically cause acute nausea and vomiting lasting up to 7 days 4

Renal/Urologic Causes

• Bilateral pyelonephritis presents with back pain (flank pain), fever, and vomiting 3
• Mechanical back pain typically does not present with urinary frequency changes, helping distinguish from urinary tract pathology 3

Neurologic Causes

• Acute migraine headaches can cause severe pain and vomiting 4, 5
• Spontaneous intracranial hypotension can present with severe headache, back pain, and vomiting, though orthostatic features are more typical 6

Metabolic/Endocrine Causes

• Metabolic and endocrine conditions should be considered when symptoms are chronic or moderate-severe 5

Malignancy

• History of cancer increases posttest probability of cancer-related back pain from 0.7% to 9% 1
• Red flags include unexplained weight loss (positive likelihood ratio 2.7), failure to improve after 1 month (positive likelihood ratio 3.0), and age >50 years (positive likelihood ratio 2.7) 1

Diagnostic Algorithm

Immediate Assessment

• Assess for red flag symptoms: urinary retention, saddle anesthesia, fecal incontinence, motor deficits, fever, recent infection, IV drug use, immunocompromised status, history of cancer, unexplained weight loss 1
• Physical examination: spine percussion for tenderness, neurologic examination including rectal tone and perianal sensation, abdominal examination for pulsatile mass 3, 1

Laboratory Studies

• Complete blood count, ESR, and CRP for suspected infection or malignancy 1
• Two sets of blood cultures if vertebral osteomyelitis suspected 3
• Lipase/amylase if pancreatitis suspected 5

Imaging

• Urgent MRI without and with contrast is recommended for suspected spinal infection, malignancy, or cauda equina syndrome 1
• Do not delay imaging in patients with suspected red flag conditions—immediate MRI is indicated rather than the usual 4-6 week waiting period for nonspecific back pain 1
• Vascular imaging (CT angiography) if aortic dissection or AAA rupture suspected 2

Critical Pitfalls to Avoid

• Missing early vertebral osteomyelitis is common—maintain high suspicion in patients with risk factors even without fever 3
• Delaying evaluation when red flag symptoms develop, particularly urinary retention, can result in permanent disability from cauda equina syndrome (prevalence 0.04% but requires immediate intervention) 1
• Assuming gastroenteritis without considering life-threatening causes when pain is severe or persistent 2
• Cauda equina syndrome is rare but requires immediate intervention to prevent permanent disability 1