Unmasking Latent Primary Hyperparathyroidism in Guillain-Barré Syndrome: A Case Report and Literature Review.

Primary hyperparathyroidism (PHPT), a common endocrine disorder, is often diagnosed in its asymptomatic stage. We report the case of a 79-year-old woman with Guillain-Barré syndrome (GBS) who developed progressive hypercalcemia, initially suspected to be immobilization hypercalcemia (IH). However, the detection of elevated intact parathyroid hormone (PTH) confirmed that the hypercalcemia was not solely due to prolonged immobilization associated with GBS but rather due to previously latent PHPT becoming clinically apparent. Treatment with elcatonin and zoledronate inhibited bone resorption, while cinacalcet suppressed PTH secretion, collectively normalizing serum calcium levels and alleviating symptoms. This case illustrates how prolonged immobilization in GBS can enhance bone resorption, leading to IH and unmasking latent PHPT. Recognizing this mechanism underscores the importance of routine calcium monitoring, PTH screening in high-risk patients, and timely intervention to prevent complications, particularly in immobilized or ageing populations.