Introduction: The "single stripe sign" (a continuous longitudinal ulceration) is widely recognized as a highly specific marker for mild ischemic colitis, particularly when observed in the left colon (descending and sigmoid segments). However, when this morphology appears outside this typical topographic distribution, alternative diagnoses must be considered. We present a case of severe Crohn's disease (CD) masquerading as ischemia through a right-sided "stripe sign."

Case Description: A 35-year-old male was admitted with fever, polyarthralgia, oral aphthae, and erythema nodosum. Laboratory workup showed anemia, elevated acute phase reactants, and high fecal calprotectin. The patient reported a history of recurrent bloody diarrhea.

Colonoscopy revealed a dual morphological pattern. The sigmoid colon showed a large, deep, excavated ulcer occupying 75% of the circumference with a fibrin-covered base, causing stenosis. Surprisingly, the right colon displayed long, linear ulcerations (>3 cm) surrounded by normal mucosa. While this longitudinal appearance strongly resembled the "single stripe sign" of ischemia, its location in the ascending colon and the patient's young age made vascular etiology highly unlikely.

Biopsies from both the right-sided "stripes" and the sigmoid ulcer confirmed chronic active inflammation compatible with Crohn's disease, ruling out ischemia, CMV, or tuberculosis.

Conclusion: This case highlights a critical diagnostic caveat: while the "single stripe sign" in the left colon is a reliable indicator of ischemia, its specificity drops precipitously when found in the right colon. In such atypical locations, especially in young patients with extraintestinal symptoms, this longitudinal ulceration represents the "railroad track" pattern of Crohn's disease. Endoscopists must integrate lesion morphology with anatomical location to avoid misdiagnosing CD as ischemia.