MM is a malignant disease characterized by clonal plasma cell proliferation in the bone marrow and is most common in the elderly . Amyloidosis is a group of diseases that involve the deposition of amyloidogenic proteins in various organs and can ultimately lead to multiple organ failure . More than 40 extracellular proteins have been identified to form amyloid in humans so far. Light-chain (AL) amyloidosis is classified as primary amyloidosis or amyloidosis secondary to myeloma , and it is the most common form of systemic amyloidosis. Approximately 10–15% of patients with MM develop overt AL amyloidosis. The incidence of AL amyloidosis significantly increases with age. It is often associated with proteinuria, cardiac amyloidosis, and peripheral neuropathy . Cowan et al. reported results from a 13-year, single-center, referral experience, which found that 76 patients (3.2%) had biopsy-proven amyloid with gastrointestinal involvement among 2334 patients with all types of amyloidosis . Among patients with systemic amyloidosis, gastrointestinal tract involvement is very common . However, only a small number of cases describing amyloidosis-induced gastrointestinal complications as the presenting symptom of MM have been reported [2,3,4,5,6,7,8,9,10,11]. In a review from the Mayo Clinic, symptomatic gastrointestinal amyloidosis had a 1% incidence in primary systemic amyloidosis . Therefore, gastrointestinal symptoms may be clinically ignored. In addition, most clinical presentations involve nonspecific GI symptoms such as abdominal pain, hemorrhage, intestinal perforation, motility disorders, and malabsorption. The most common endoscopic presentations of AL type amyloidosis within the luminal gastrointestinal tract are mucosal erosions, ulcerations, and submucosal hematomas , and fine granular and polypoid protrusions . Amyloid deposits may also cause recurrent peptic ulcers; thus, gastric amyloidosis may also present as gastric dysplasia.
It remains a challenge to draw an accurate diagnosis of MM. In our case, anemia, alimentary symptoms, and melena were the chief complaints. EGD revealed gastric retention and a gastric antrum mucosal bulge with surface erosion. Because of these misleading manifestations, we misinterpreted the signs of a systemic disease as including skeletal Rx-lesions, renal failure, and higher circulating immunoglobulin levels. The first pathological examination without special staining initially indicated chronic superficial gastritis (mild). However, follow-up pathological examination led to a definite diagnosis of gastric amyloidosis through positive Congo red staining and bone marrow biopsy.
For patients with digestive system symptoms and nonspecific endoscopic features, it is important to consider the diagnosis of amyloidosis and a biopsy with Congo red staining should be performed for the precise diagnosis for GI amyloidosis. After amyloidosis is confirmed, immunoglobulin free light chain κ and λ testing, bone marrow biopsy, serum and urine immunofixation, echocardiography, 24-h urine total protein test, and quantitative immunoglobulin measurement should be performed  to assess the underlying disorder. The treatment and prognosis of amyloidosis depend on whether patients have systemic or localized disease. The severity of cardiac dysfunction at the time of diagnosis is a determinant of the survival of patients with systemic AL amyloidosis [21, 22].
Drug therapy for AL amyloidosis includes conventional chemotherapy such as melphalan or prednisolone and some novel drugs that include proteasome inhibitors and immunomodulatory drugs . For most AL patients, the pathological clone of plasma cells is relatively benign and various drugs can be effective. Nevertheless, they are often poorly tolerated because of damaged organ function. Thus, as reported in this case, treatments for the elderly are delayed because of their poor general condition that does not allow chemotherapy to be performed. One retrospective study found that the time from symptom onset to diagnosis was 7–24 months . Part of the reason for this delay is the overall rarity of the disease. Early accurate diagnosis is possible if doctors can associate nonspecific clinical symptoms with multiple systemic data and establish close communication with pathologists.
In conclusion, this case highlights the importance of a clinical suspicion of gastric amyloidosis in patients with nonspecific GI symptoms such as vomiting or melaena. In addition, endoscopic biopsy with Congo red staining should be performed for differentiating between amyloidosis and cancer because of the similar endoscopic features of the two condition. Early diagnosis and treatment are essential for patients with gastric amyloidosis because of its severity and poor prognosis.