Does Increased Body Mass Index Predispose Myeloma Patients to Fractures or Shortened Survival?.

Background: Obese individuals are at increased risk of developing myeloma (Pan et al, Am J of Epidemiol, 2004, Feb) and at increased risk of death, compared to non-obese individuals (Calle et al, N Engl J Med, 2003 April). However, a higher BMI is protective against the development of osteoporosis and fracture in the general population (Siris et al, JAMA, 2001 Dec).

Objectives: To assess the effect of obesity on fracture risk and mortality in patients diagnosed with multiple myeloma.

Patients and Methods: Retrospective chart review of all patients identified by the Tumor Registry with the diagnosis of multiple myeloma, diagnosed from 1999–2003, at a single center (n= 60). Median age: 66 (range: 39–91). The study group is comprised of the following characteristics: female (58%), African-American (82%), white (15%) and other races (3%). All patients with bone disease were treated with bisphosphonates.

Results: According to the World Health Organization criteria for BMI, 32% were grade 1 obese (25–29.9kg/m²), 18% were grade 2 obese (30–34.9kg/m²), 13% were grade 3 or 4 obese (>35kg/m).² Fracture occurred in 23 patients (38%), either at diagnosis or during follow up. The mean BMI of patients with fracture was 30.7 ± 7.2 kg/m ^2. The mean BMI of patients without fracture was 26.5 ± 4.2 kg/m ^2.T-test comparison between the 2 groups shows a statistically significant correlation between increased BMI and fracture occurrence (T value = 2.577, p= 0.013). Rank-Spearman correlation was used to assess the significance of age, gender and diabetes as confounding factors; none of these factors were shown contribute to the difference observed. This correlation also shows statistically significant correlation between increased BMI and number of fractures (p= 0.035). Mean BMI of patients with rib fractures was 27.7kg/m² (N=6), vertebral compression fractures was 31.8 (N=13), pathologic femur fractures was 30.3 (N=5) and all other types was 27.0 (N=4). The BMI is numerically greater in patients with fractures of weight bearing bones, but this difference did not reach statistical significance. Of the 60 patients studied, 27 patients have died. The median survival of patients with a normal BMI (<25 kg/m²) was 50 months, and that of patients with an increased BMI (≥25 kg/m²) was 58 months (p>0.05). Patients with poor performance status experienced shorter survival (p= 0.013).

Conclusions: Although a higher BMI is protective against the development of osteoporosis in the general population, our study shows that higher BMI correlates with a greater incidence of osteoporosis and fracture in patients with multiple myeloma. Our results suggest that reduction of BMI should be recommended to reduce the likelihood of fracture and related complications. Prospective studies of larger populations to assess the impact of BMI and weight loss on fracture development are needed. BMI does not appear to impact on the length of survival of these patients. Limitations of this study include its retrospective nature, small sample size, ethnic distribution and location at a single institution.