Misdiagnosis of multiple myeloma as postoperative bone metastasis of rectal cancer: A case report and literature review.

Multiple myeloma (MM) and bone metastases are both common malignant tumors of the skeleton that share similar clinical manifestations and radiological features. The development of MM following rectal cancer surgery is relatively rare in clinical practice and is easily misdiagnosed as bone metastasis. The present study reported on a patient with MM and postoperative rectal cancer. A 65-year-old man had been diagnosed with low rectal cancer (poorly differentiated, T3N1M0) 10 years prior and underwent curative treatment at that time. During the 6-year follow-up period, no recurrence or metastasis of rectal cancer was detected. The patient was evaluated for bone pain 4 years ago and underwent multiple imaging examinations, including computed tomography (CT), magnetic resonance imaging, emission CT and positron emission tomography/CT at several well-known hospitals in China. All of these hospitals diagnosed the patient with bone metastasis from rectal cancer, in view of the earlier history. The patient's condition did not show any significant improvement despite treatment for bone metastasis. Subsequently, 3 years ago, the patient underwent surgical treatment at our hospital (Affiliated Hospital of Zunyi Medical University, Zunyi, China) for a hernia near the colostomy site combined with incomplete intestinal obstruction. Post-operatively, the patient developed a hematoma in the surgical area, along with stubborn anemia and abnormal coagulation function. No improvement was observed with hemostasis and multiple blood transfusions. The bone marrow smear was consistent with MM, with a significant elevation in serum IgA and β2 microglobulin. The patient was ultimately diagnosed with MM (IgA-λ type), stage III, according to the Durie-Salmon staging system. The patient's condition improved with treatment for MM.