The Relationship between the Abnormalities in Electroencephalogram and Blood Levels of Parathyroid Hormone in Dialysis Patients*

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Abstract
Clinical and experimental data indicate that both acute and chronic uremia with excess circulating parathyroid hormone (PTH) levels are associated with a marked abnormality of the electroencephalogram (EEG); the latter may be related to the degree of hyperparathyroidism. The present study examines this question in 20 dialysis patients. All had slowing of the EEG, evidenced by significant (P < 0.01) increases [10.7–23.1% mean, 16.1 ± 0.8% (SE)] in EEG frequency below 7 Hz (normal, 2.3 ± 0.3). There was no correlation between the degree of slowing of the EEG and serum calcium, phosphorus, or creatinine levels, age, or duration of dialysis, but a significant and direct relationship existed with serum levels of the N-terminal fragment of PTH (N-PTH; r = 0.61; P < 0.01), though not with serum levels of the C-terminal moiety (C-PTH). Six months of treatment with 1,25-dihydroxyvitamin D3 produced a marked fall in NPTH from 4283 ± 614 to 1738 ± 487 pg/ml (normal, <250) in 6 of 8 patients; this fall was associated with significant (P < 0.01) improvement in the percentage of EEG frequency below 7 Hz (from 17.5 ± 1.5% to 8.7 ± 0.9%). In the 2 patients in whom NPTH did not fall, the EEG did not improve. In 6 patients in whom serum C-PTH fell progressively, improvement in EEG occurred. Parathyroidectomy was followed by normalization of N-PTH, C-PTH, and EEG. The data suggest that: 1) a direct relationship exists between EEG abnormality and serum NPTH, and 2) amelioration of hyperparathyroidism, as evidenced by a fall in N-PTH or C-PTH, is associated with improvement or normalization of EEG. The results suggest a neurotoxic but reversible effect of PTH in uremia.