A 75-year-old man has complained of lower back pain for years. As pa of a investigation for a persistently elevated lymphocytosis, he had a right posterior iliac crest biopsy performed. Hematopoiesis is normal, but the bone spicules are thickened with irregular cement lines forming a mosaic appearance with both increased osteoblastic and osteoclastic activity. Which of the following conditions is most likely to occur in conjunction with this disease process?