Differential Diagnosis for Elevated ALP, PTH, and LDH in a 16-Year-Old Male

Single Most Likely Diagnosis

• Primary Hyperparathyroidism: This condition, characterized by an overproduction of parathyroid hormone (PTH), can lead to elevated alkaline phosphatase (ALP) due to increased bone turnover. The elevated PTH directly points towards this diagnosis, and the elevated LDH could be seen in the context of increased bone resorption.

Other Likely Diagnoses

• Vitamin D Deficiency: A deficiency in vitamin D can lead to secondary hyperparathyroidism, where PTH is elevated in response to low vitamin D levels. This can cause an increase in ALP due to the body's attempt to mobilize calcium from the bones. LDH elevation can be seen in various metabolic states, including those affecting bone metabolism.
• Paget's Disease of Bone: Although rare in teenagers, this condition involves an abnormal breakdown and regrowth of bone tissue, leading to elevated ALP and potentially PTH and LDH due to the high bone turnover rate.
• Hyperthyroidism: Can lead to increased bone turnover, thus elevating ALP and potentially affecting PTH and LDH levels indirectly through its effects on bone metabolism.

Do Not Miss Diagnoses

• Malignancy (e.g., Lymphoma, Leukemia): Certain cancers can cause elevations in LDH, and if they involve bone, could also affect ALP and PTH. It's crucial to consider malignancy due to its severe implications and the need for prompt treatment.
• Sarcoidosis: A condition that can affect multiple systems, including the bones and parathyroid glands, leading to elevations in ALP, PTH, and potentially LDH due to granulomatous disease.
• Familial Hypocalciuric Hypercalcemia (FHH): A genetic disorder that affects calcium sensing by the parathyroid glands, leading to hyperparathyroidism. It's essential to distinguish this from primary hyperparathyroidism due to its different management approach.

Rare Diagnoses

• Osteogenesis Imperfecta: A genetic disorder characterized by fragile bones, which could lead to elevated ALP due to bone fractures and remodeling. However, the direct link to elevated PTH and LDH is less clear unless there's a significant fracture or bone disease component.
• Juvenile Hyperparathyroidism: A rare condition in adolescents, similar to primary hyperparathyroidism but with a potential for more severe symptoms and a familial component.