What happened, in summary

A 77-year-old man sought care after 4 weeks of an intensely itchy blistering rash and generalized weakness. The rash began on his abdomen and spread across his trunk and limbs, producing tense blisters and superficial sores. He had no fever, pain, or recent medication change that clearly explained it. Skin biopsies confirmed bullous pemphigoid, an autoimmune blistering condition.

He also reported black stools and diarrhea that had continued for about 3 years. Blood tests showed iron-deficiency anemia, including a hemoglobin level of 9.2 g/dL and ferritin of 12 ng/mL. Over 6 weeks, he needed several red-blood-cell transfusions. These gastrointestinal symptoms and the anemia prompted a search for an underlying cause.

Colonoscopy found a 5 cm circumferential ulcerated mass in the rectosigmoid colon. Biopsy showed moderately differentiated invasive adenocarcinoma. CT imaging showed thickening of the sigmoid-colon wall but no distant metastasis.

The skin disease was initially treated with doxycycline, niacinamide, and topical triamcinolone and clobetasol. His blisters began to improve. He then underwent surgical removal of the rectosigmoid cancer. Within 6 weeks after cancer surgery, the bullous lesions had completely resolved, and he remained off dermatologic treatment without recurrence of the rash. The improvement raised the possibility that the skin condition was linked to the cancer. However, he was lost to follow-up after discharge, so his longer-term colorectal-cancer outcome was not established.

His skin and bowel problems had developed on very different timelines, but cancer surgery was followed by complete clearing of the blisters.