A 65-year-old male with 25-year history of hypertension (HTN) presents with poor appetite and fatigue for over 3 months. Examination: BP 195/98 mmHg, apathy, questionable flapping tremor (asterixis) in upper limbs, intermittent involuntary movements in lower limbs, bilateral ankle clonus (+). Normal liver function. Lab: serum creatinine 1000 μmol/L, hemoglobin (Hb) 65 g/L, serum calcium (Ca) 1.9 mmol/L, serum phosphorus (P) 3.0 mmol/L, serum potassium (K) 5.5 mmol/L, CO₂CP 18 mmol/L. The most likely cause of neurological changes is: