In patients presenting with classical findings of primary hyperparathyroidism (i.e mild hypercalcemia, high 24hr urine calcium, elevated 1,25 Vit D but normal PTH), can spontaneous normalization of calcium be explained by episodic hypersecretion of PTH?

PTH secretion is always about 70% basal, related to the mass of parathyroid tissue, and about 30% episodic. Patients with primary hyperparathyroidism can have superimposed secondary hyperparathyroidism. High urinary calcium suggests a negative calcium balance.

PTH is not "normal" if calcium levels are high. It should be suppressed. Total calcium levels can be deceptive. If possible, fasting ionized calcium should be measured.