Gastrointestinal amyloidosis in a patient with smoldering multiple myeloma: A case report

BACKGROUND: Smoldering multiple myeloma (SMM) is an asymptomatic plasma cell proliferative disorder that can progress to multiple myeloma (MM). Amyloidosis (light chain) (AL) is the most common form of systemic amyloidosis. There are few reports of SMM coexisting with AL involving the digestive tract. CASE SUMMARY: A 63-year-old woman presented with lower limb edema, abdominal distension, abdominal pain, and hematochezia. Gastroscopy showed gastric retention, gastric angler mucosal coarseness, hyperemia, and mild oozing of blood. Colonoscopy showed hyperemic and edematous mucosa of the distal ascending colon and sigmoid colon with the presence of multiple round and irregular ulcers, submucosal ecchymosis, and hematoma. Gastric and colonic tissue biopsy confirmed the diagnosis of AL by positive Congo red staining. MM was confirmed by bone marrow biopsy and immunohistochemistry. The patient had no hypercalcemia, renal dysfunction, anemia, bone lesions or biomarkers of malignancy defined as plasma cells > 60% in bone marrow. Additionally, no elevated serum free light chain ratio, or presence of bone marrow lesions by magnetic resonance imaging (SLiM criteria) were detected. The patient was finally diagnosed with SMM coexisting with AL. She received chemotherapy and was discharged when the symptoms were relieved. She is doing well at nearly five years of follow up. CONCLUSION: This case highlights that high index of suspicion is required to diagnose gastrointestinal AL. It should be suspected in elderly patients with endoscopic findings of granular-appearing mucosa, ecchymosis, and submucosal hematoma. Timely diagnosis and appropriate therapy can help to improve the prognosis of these patients.