Chapter 39: Unintentional Weight Loss or Gain Evaluation

Unintentional Weight Loss or Gain Evaluation explores the physiological mechanisms governing weight fluctuation, including shifts in body fluid, muscle mass, and fat stores, as well as the fundamental balance between caloric intake and basal metabolic rate (BMR). The text provides an extensive differential diagnosis for unintentional weight loss, categorized into malignancies (causing cachexia), endocrine disorders (such as hyperthyroidism and Type 1 diabetes mellitus), gastrointestinal conditions (including malabsorption, celiac disease, and Crohn disease), and chronic infections like tuberculosis and HIV/AIDS. It also addresses psychosocial etiologies, specifically anorexia nervosa and depression. Conversely, the chapter analyzes causes of unexplained weight gain, such as hypothyroidism (myxedema), Cushing syndrome (characterized by truncal obesity and moon facies), medication side effects (including corticosteroids and antidepressants), and lifestyle factors contributing to obesity. Special attention is given to pediatric populations, covering failure to thrive, breastfeeding adequacy, and cystic fibrosis, as well as geriatric syndromes like frailty and dementia. The diagnostic reasoning process is detailed through focused history taking—assessing appetite, dietary habits, and physical activity—and a comprehensive physical examination that includes thyroid palpation, assessment of hydration status, and screening for malignancy. Finally, the chapter outlines essential diagnostic studies, including complete blood counts, thyroid-stimulating hormone (TSH) levels, fasting blood glucose, glycosylated hemoglobin (A1c), sweat chloride tests, and cancer screenings, while integrating evidence-based guidelines from the USPSTF regarding obesity screening and behavioral interventions.