The Hidden Iceberg of ADPKD: Early Organomegaly-Driven Malnutrition and Sarcopenia Beyond Preserved eGFR

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent monogenic kidney disease (≈4 cases per 10.000 inhabitants) and a major cause of end-stage kidney disease (ESKD). Beyond progressive cystic enlargement of the kidneys and frequent extrarenal involvement, adults with ADPKD often exhibit a distinctive "body phenotype" with central adiposity and marked abdominal distension due to renal and hepatic organomegaly. In this setting, conventional anthropometric indices such as body mass index (BMI) and crude body weight are of limited value, as they cannot distinguish nutritional tissues (muscle, subcutaneous fat) from non-nutritional mass (cyst fluid, fibrotic tissue, or expanded extracellular water). This review summarizes the current evidence on malnutrition and sarcopenia in adult ADPKD, with a focus on the impact of organomegaly and adiposity. Cross-sectional work using the modified Subjective Global Assessment (SGA) has shown that approximately one-third of ambulatory ADPKD patients are at risk of becoming, or have become, malnourished, and that height-adjusted total kidney and liver volume (htTKLV) is the strongest clinical predictor of malnutrition, whereas eGFR plays a secondary role. Bioelectrical impedance analysis (BIA) further demonstrates a disease-specific body composition phenotype, with increased total and extracellular body water, particularly in the trunk, a reduced phase angle and reduced lean mass, consistent with early malnutrition and sarcopenia. These alterations are present even at relatively preserved kidney function and, in matched analyses, distinguish ADPKD from non-ADPKD CKD. Prospective data from a multicenter cohort indicate that the baseline SGA-defined nutritional status independently predicts short-term eGFR decline in typical ADPKD, supporting malnutrition as a potential modifier of renal trajectory rather than a mere correlate of advanced disease. In parallel, narrative syntheses on adiposity highlight that a higher BMI, waist circumference and visceral fat are associated with larger total kidney volume, faster eGFR loss and greater symptom burden, and raise concern for a sarcopenic obesity phenotype in which excess fat and cystic mass coexist with low muscle mass. Collectively, these findings support a pathophysiological model in which organomegaly-driven mechanical effects (early satiety, gastrointestinal discomfort), systemic inflammation, insulin resistance and cyst-related metabolic reprogramming converge to produce "hidden malnutrition" in ADPKD, masked by apparent overweight. From a clinical perspective, malnutrition and sarcopenia should be regarded as central, disease-modifying components of the ADPKD phenotype. Routine nutritional screening (e.g., SGA/PG-SGA) and BIA-based body composition assessment, particularly in patients with severe organomegaly or symptomatic polycystic liver disease, should be integrated into ADPKD care pathways, and individualized, muscle-preserving nutritional strategies should be tested in future prospective studies.