Extensive Parenchymal Brain Calcification in a Patient With Autosomal Dominant Polycystic Kidney Disease and Stage 5 Chronic Kidney Disease.

Extensive parenchymal brain calcification is uncommon in chronic kidney disease (CKD): intracranial vascular calcification affects up to 10% of uremic patients, but widespread Fahr-type parenchymal deposits are rare and, where reported, have occurred in patients with a coexisting hypoparathyroid or parathyroid-hormone (PTH)-resistant state. We describe a man in his 50s with autosomal dominant polycystic kidney disease (ADPKD) and Stage 5 CKD who presented with word-finding difficulty, gait imbalance, and myoclonus and was found to have extensive symmetric calcification of the basal ganglia, thalami, dentate nuclei, and subcortical white matter. He carried an unverified childhood diagnosis of pseudohypoparathyroidism made at age 13. At presentation, total calcium was 6.1-6.3 mg/dL, phosphate 5.8 mg/dL, intact PTH 194 pg/mL, creatinine 6.21 mg/dL, and alkaline phosphatase normal. Over the following 10 months, intact PTH fell rather than rose, reaching 56 pg/mL during treatment with calcium, calcitriol, sevelamer, and hemodialysis, all of which lower PTH whatever the underlying cause. The calcium-phosphate product was low at presentation (36.5 mg2/dL2) but rose to 58-62 mg2/dL2 later, and single values cannot exclude earlier CKD-related mineral abnormality. No pathogenic variant was identified on an 866-gene panel. Neither the product nor the PTH trajectory separated renal from non-renal contributions. We present this as a diagnostic-reasoning case that raises, but cannot resolve, the question of causation and suggest that such calcification should not be attributed to CKD-mineral and bone disorder by default.