Which autoimmune conditions can present with unexplained abdominal pain, dyspnea, and a non‑healing ulcer on the left anterior shin?

Autoimmune Conditions Presenting with Abdominal Pain, Dyspnea, and Shin Ulceration

The most likely autoimmune diagnoses to consider are systemic vasculitis (particularly ANCA-associated vasculitis such as granulomatosis with polyangiitis), inflammatory bowel disease with extra-intestinal manifestations (specifically pyoderma gangrenosum), and systemic lupus erythematosus. 1

Primary Differential Diagnoses

Systemic Vasculitis

• All vessel-sized vasculitis can present with abdominal pain, dyspnea from pulmonary involvement, and skin manifestations including digital necrosis and ulceration on the extremities 1
• Granulomatosis with polyangiitis (formerly Wegener's) specifically causes respiratory symptoms (dyspnea), can involve the gastrointestinal tract causing abdominal pain, and produces skin ulcers 1
• Critical caveat: ANCA antibodies (particularly anti-PR3) are often positive but may be absent in some cases, so negative serology does not exclude the diagnosis 1
• Look for: constitutional symptoms (fever, fatigue), purpura, arthralgias, and evidence of multi-organ involvement 1

Inflammatory Bowel Disease with Pyoderma Gangrenosum

• Pyoderma gangrenosum (PG) occurs in 0.6–2.1% of ulcerative colitis patients and presents as deep excavating ulcers with violaceous edges, most commonly on the shins 1
• The shin location matches the classic distribution for PG, which preferentially affects the anterior tibial areas and areas adjacent to stomas 1
• Abdominal pain would reflect active IBD, while dyspnea could indicate pulmonary involvement or pleural effusions (pericardial involvement occurs in inflammatory bowel diseases) 1
• Key diagnostic feature: The ulcer typically starts as a pustule that rapidly becomes a burrowing ulcer exposing deep tissues, with sterile purulent material unless secondarily infected 1
• PG may parallel IBD activity or run an independent course 1

Systemic Lupus Erythematosus

• SLE commonly causes abdominal pain (occurring in up to 50% of patients) through multiple mechanisms including peritonitis from polyserositis, mesenteric ischemia, or conventional surgical pathology 2, 3
• Dyspnea results from pleural effusions (very common in SLE), pulmonary involvement, or pericardial disease 3
• Skin ulceration can occur, though less characteristic than the malar rash 4
• Diagnostic approach: Check ANA (optimal at 1:320 threshold with 95.8% sensitivity), anti-dsDNA (highly specific), and anti-Smith antibodies 4
• Look for cytopenias (anemia, leukopenia, thrombocytopenia), hypocomplementemia (low C3/C4), and urinalysis showing proteinuria or cellular casts suggesting lupus nephritis 4, 3

Less Likely but Important Considerations

Behçet's Disease

• Can cause abdominal pain (gastrointestinal involvement), dyspnea (pulmonary vasculitis), and skin ulceration 1, 5
• Distinguishing features: Look for oral and genital ulcers, which are hallmark features 5
• Erythema nodosum may be the dominant skin lesion rather than true ulceration 5

Sarcoidosis

• Presents with dyspnea (pulmonary involvement with hilar lymphadenopathy), can cause abdominal pain, and produces skin nodules 1
• Key distinction: Skin manifestations are typically nodules or plaques rather than ulcers, and diagnosis requires biopsy showing non-caseating granulomas 1
• Löfgren's syndrome (bilateral hilar adenopathy with erythema nodosum and arthritis) has excellent prognosis 5

Critical Diagnostic Algorithm

Step 1: Characterize the Shin Lesion

• If violaceous undermined edges with purulent base: Strongly suggests pyoderma gangrenosum; biopsy the periphery to exclude other diagnoses and evaluate for IBD 1
• If migratory subcutaneous nodules: Consider gnathostomiasis (requires travel history to Southeast Asia) or erythema nodosum 6, 5
• If fixed tender nodules on anterior tibial areas: Suggests erythema nodosum, which is associated with IBD, sarcoidosis, or Behçet's disease 1, 5

Step 2: Assess Respiratory Symptoms

• Obtain chest imaging to evaluate for pleural effusions (SLE, serositis), pulmonary nodules (vasculitis, sarcoidosis), or hilar lymphadenopathy (sarcoidosis) 1, 3
• Pulmonary function tests if interstitial lung disease suspected 1

Step 3: Laboratory Evaluation

• Initial serologies: ANA (if ≥1:320, proceed with anti-dsDNA and anti-Smith for SLE), ANCA (c-ANCA/PR3 and p-ANCA/MPO for vasculitis), RF (often negative in these conditions) 1, 4
• Complete blood count: Look for cytopenias (SLE), eosinophilia (rare in these conditions but may suggest parasitic infection) 4
• Inflammatory markers: ESR and CRP (elevated in active disease but non-specific) 1
• Complement levels: Low C3/C4 suggests SLE; isolated C4 elevation is not characteristic of these conditions 4
• Urinalysis with microscopy: Essential to detect lupus nephritis (proteinuria, cellular casts) 4

Step 4: Gastrointestinal Evaluation

• If diarrhea, bloody stools, or chronic symptoms: Colonoscopy to evaluate for IBD 1
• If acute severe pain: CT abdomen to exclude mesenteric ischemia (vasculitis, SLE), perforation, or conventional surgical pathology 2
• Important caveat: In SLE patients presenting to community hospitals, most abdominal pain is from conventional surgical conditions (cholecystitis, perforated ulcer, diverticulitis) rather than lupus-specific causes 2

Common Pitfalls to Avoid

• Do not dismiss negative autoantibodies: Vasculitis can present with negative ANCA, and early SLE may have fluctuating or initially negative serologies 1, 3
• Do not assume all abdominal pain in autoimmune disease is disease-specific: Conventional surgical pathology (appendicitis, cholecystitis, perforation) remains common and requires standard surgical evaluation 2
• Do not biopsy typical erythema nodosum: Clinical diagnosis is sufficient for characteristic bilateral anterior tibial nodules; reserve biopsy for atypical presentations 1, 5
• Do not delay rheumatology consultation: Early specialist involvement improves diagnostic accuracy and prevents treatment delays 1
• Do not overlook infectious mimics: Exclude tuberculosis before starting immunosuppression, and consider endemic fungi (coccidioidomycosis, histoplasmosis) or parasites (gnathostomiasis) based on exposure history 6, 5

Treatment Considerations

• Pyoderma gangrenosum: Systemic corticosteroids, infliximab, or adalimumab; topical or oral calcineurin inhibitors for localized disease 1
• Vasculitis: Requires aggressive immunosuppression with corticosteroids plus cyclophosphamide or rituximab; consult rheumatology urgently 1
• SLE: Hydroxychloroquine as baseline therapy, corticosteroids for acute flares, and immunosuppressants (azathioprine, mycophenolate) for organ-threatening disease 4
• IBD-associated manifestations: Treat underlying IBD; TNF-alpha inhibitors effective for both intestinal and extra-intestinal manifestations 1