Impact of Hypothyroidism on Muscle Mass and Spine Deformity in Adult Spinal Deformity: A Retrospective Analysis

Introduction: Hypothyroidism, marked by reduced thyroid hormone production, affects multiple physiological systems, including muscle health. Its relationship with sarcopenia in adult spinal deformity (ASD) patients is not well understood. Clarifying this link could improve sarcopenia management and outcomes in ASD.

Methods: We retrospectively analyzed consecutive ASD patients who underwent long-segment fusion at a tertiary care center from 2016 to 2021. Thyroid-stimulating hormone (TSH) and thyroxine (T4) levels were averaged over 10 years preoperatively and 1 year postoperatively. Hypothyroidism was defined by TSH >4.5mIU/L, T4 < 0.9 ng/dL, or the need for thyroid replacement therapy. Regression models, adjusted for age, gender, and BMI, analyzed associations between thyroid function, Psoas Muscle Index (PMI) at the L3 and L4 levels, and spinal deformity (cobb angle, sagittal vertical axis, pelvic tilt).

Results: 235 ASD patients were included (M=80, F=155), of whom 82 were hypothyroid (F=65, M=17). Hypothyroid patients had significantly lower PMI compared to non-hypothyroid patients at the L3 and L4 level (L4: 637.0 mm2/m2 vs. 750.7 mm2/m2, p = 1.07E-05; L3: 440.2 mm2/m2 vs. 535.4 mm2/m2, p = 1.21E-06). TSH and T4 levels were not correlated with spine deformity measures or PMI values (p > 0.05).

Conclusion : Hypothyroid ASD patients exhibit reduced muscle mass relative to non-hypothyroid ASD patients. While no direct correlation was observed between thyroid levels and spinal deformity measures, these findings suggest that muscle health assessment may be relevant in managing hypothyroid ASD patients. Further studies are warranted to clarify these relationships.