Primary Hyperparathyroidism: This condition is characterized by elevated parathyroid hormone (PTH) levels and hypercalcemia, which matches the patient's presentation. The normal urine calcium and negative parathyroid adenoma on ultrasound do not rule out primary hyperparathyroidism, as it can be caused by parathyroid hyperplasia or a small adenoma not detected by ultrasound.

Vitamin D Deficiency: Although the patient has a low vitamin D level, this typically leads to secondary hyperparathyroidism with low or normal calcium levels, not elevated calcium. However, it's essential to correct the vitamin D deficiency to assess its impact on PTH and calcium levels.
Familial Hypocalciuric Hypercalcemia (FHH): This condition is characterized by elevated PTH and calcium levels with low urinary calcium excretion, which fits the patient's presentation. Genetic testing can help confirm this diagnosis.

Malignancy-Associated Hypercalcemia: Hypercalcemia of malignancy can be caused by PTH-related protein (PTHrP) production by tumors, which can mimic primary hyperparathyroidism. A thorough evaluation for underlying malignancy is crucial, especially in patients with unexplained hypercalcemia.
Hypercalcemia of Granulomatous Diseases: Conditions like sarcoidosis can cause hypercalcemia due to increased vitamin D production. Although the patient's vitamin D level is low, this condition should be considered, especially if other symptoms are present.

Lithium-Induced Hyperparathyroidism: Lithium therapy can cause hyperparathyroidism, leading to elevated PTH and calcium levels. A detailed medication history is necessary to consider this diagnosis.
Multiple Endocrine Neoplasia (MEN) Syndromes: These syndromes can include primary hyperparathyroidism as a component. Although rare, they should be considered in patients with a family history or other endocrine abnormalities.