Hyperparathyroidism is a common cause of hypercalcemia and the effects of calcium at the neuromuscular junction may cause pre-existing muscle weakness. However, this response is unpredictable and though it might seem that the pre-existing muscle weakness associated with hyperparathyroidism would reduce neuromuscular blocker requirements, it has been suggested that hypercalcemia associated with primary HPT may antagonize the effects of non-depolarizing muscle relaxants, making patients more resitant to blockade.
In one study, hypercalcemia was associated with decreased sensitivity to atracurium and thus a shortened time course of neuromuscular blockade. The strongly suggests that patients would be more resistant to neuromuscular blockade.
Nevertheless, it is advised that neuromuscular blockade be carefully titrated to effect.
S Al-Mohaya, M Naguib, M Abdelatif, H Farag Abnormal responses to muscle relaxants in a patient with primary hyperparathyroidism. Anesthesiology: 1986, 65(5);554-6