What is the differential diagnosis and management plan for a young adult with a history of ankylosing spondylitis (AS) presenting with severe epigastric pain and a soft abdomen, without current medication use?

Differential Diagnosis and Management for Severe Epigastric Pain in Ankylosing Spondylitis

Immediate Differential Diagnosis

The most critical diagnoses to exclude immediately are peptic ulcer disease with or without perforation, acute pancreatitis, and inflammatory bowel disease (IBD), as these are directly associated with AS and carry significant morbidity if missed. 1

High-Priority Gastrointestinal Causes

• Peptic ulcer disease or gastritis is the leading concern given the AS diagnosis, as NSAIDs (first-line AS treatment) cause dose-dependent GI bleeding risk (RR 5.36 for serious GI events), even though this patient reports no current medication use 2
• Inflammatory bowel disease (IBD) must be urgently evaluated, as silent IBD is frequent in AS patients and spondylarthritis may be the first manifestation of IBD 1, 3
• Acute pancreatitis should be considered given the severity of pain (10/10) and AS association with systemic inflammation 1

Other Important Considerations

• Reactivation tuberculosis with abdominal involvement can present with severe abdominal pain in AS patients, particularly if they have received immunosuppressive therapy in the past 3
• Cardiac causes (inferior MI presenting as epigastric pain) warrant evaluation given AS patients have increased cardiovascular disease risk 2
• Enthesitis of the anterior chest wall or costovertebral joints can occasionally present as epigastric discomfort, though 10/10 pain severity makes this less likely 4

Immediate Diagnostic Workup

Laboratory Studies (Obtain Immediately)

• Complete blood count to assess for anemia (chronic GI bleeding), leukocytosis (infection, perforation), or thrombocytosis (inflammation) 2
• Comprehensive metabolic panel including liver enzymes and renal function 2
• Lipase and amylase to rule out pancreatitis 2
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to assess inflammatory activity 2
• Troponin given cardiovascular risk in AS and atypical presentation possibility 2
• Stool studies including fecal calprotectin if IBD suspected 1

Imaging Studies

• Upright chest X-ray and abdominal X-ray immediately to exclude free air under the diaphragm (perforated viscus) 2
• CT abdomen/pelvis with IV contrast if initial labs or X-rays are concerning, or if pain persists without clear diagnosis 2
• Upper endoscopy should be arranged urgently if peptic ulcer disease is suspected based on clinical presentation and initial workup 2

Immediate Management Algorithm

Step 1: Stabilization and Symptom Control (First 30 Minutes)

• NPO status until perforation and surgical abdomen are excluded
• IV access and fluid resuscitation with normal saline
• Avoid NSAIDs completely given GI risk profile and diagnostic uncertainty 2
• Provide analgesia with IV opioids (morphine or hydromorphone) as paracetamol alone will be insufficient for 10/10 pain 2, 5
• Proton pump inhibitor (PPI) IV (pantoprazole 40mg or esomeprazole 40mg) should be started immediately given high suspicion for peptic disease 2

Step 2: Risk Stratification Based on Initial Assessment

If peritoneal signs develop or imaging shows perforation:

• Immediate surgical consultation for potential perforated viscus
• Keep NPO, place nasogastric tube, broad-spectrum IV antibiotics

If no peritoneal signs but severe pain persists:

• Proceed with CT abdomen/pelvis with contrast
• Gastroenterology consultation for urgent endoscopy within 24 hours
• Continue IV PPI therapy

If pain improves with initial management:

• Transition to oral PPI (omeprazole 40mg twice daily or equivalent)
• Schedule outpatient upper endoscopy within 1-2 weeks
• Arrange gastroenterology and rheumatology follow-up

Step 3: Address Underlying AS Management

Once acute abdomen is excluded, initiate appropriate AS treatment:

• NSAIDs remain first-line for AS pain management but must be selected carefully given this GI event 2, 5
• If peptic ulcer disease is confirmed, use selective COX-2 inhibitor (celecoxib) plus high-dose PPI (reduces serious GI events by 82% compared to traditional NSAIDs, RR 0.18) once ulcer is healed 2, 5
• If IBD is diagnosed, coordinate with gastroenterology; monoclonal antibody TNF inhibitors (infliximab or adalimumab) are strongly preferred over etanercept for combined AS-IBD management 6, 1
• Initiate physical therapy immediately as non-pharmacological treatment is essential and complementary to drug therapy throughout AS disease course 2, 6

Critical Management Pitfalls to Avoid

• Do not assume the soft abdomen excludes serious pathology - early perforation or ischemia may not show peritoneal signs initially
• Do not restart NSAIDs without gastric protection if any GI pathology is identified, as continuous NSAID use without protection carries RR 5.36 for serious GI events 2
• Do not use systemic corticosteroids for AS axial disease as they are contraindicated due to lack of efficacy and significant side effects 6
• Do not delay endoscopy if peptic ulcer disease is suspected, as AS patients may have silent progression given their chronic inflammatory state 1
• Do not overlook IBD screening even if initial presentation seems purely gastric, as 10-15% of AS patients have associated IBD that may be subclinical 1, 3

Long-Term AS Management After Acute Episode Resolution

• Continuous NSAID therapy is preferred over on-demand use for persistently active AS, as it may retard radiographic progression 5, 6
• Group physical therapy demonstrates superior outcomes compared to home exercise alone for patient global assessment 6
• Monitor for extra-articular manifestations including uveitis (most common), cardiac involvement, and pulmonary disease 2, 1
• If NSAIDs plus gastroprotection are insufficient or contraindicated, consider TNF inhibitor therapy for persistently high disease activity 5, 6