If a patient’s phosphorous levels are normal but alkaline phosphatase is elevated, what is the likely diagnosis?

When alkaline phosphatase levels are elevated while phosphorous levels remain normal, it suggests increased bone turnover or activity, which is characteristic of Paget’s disease. This condition is marked by abnormal bone remodeling, leading to enlarged and weakened bones. The elevated alkaline phosphatase reflects increased osteoblastic activity as the bone is being remodeled excessively.

In contrast, conditions like osteoporosis typically do not present with significantly elevated alkaline phosphatase. Osteoporosis is more associated with decreased bone mass and structural deterioration rather than with heightened enzyme levels. Vitamin D deficiency usually leads to both low phosphorous and alkaline phosphatase levels, as it can cause osteomalacia and affect bone mineralization. Similarly, hyperparathyroidism may increase alkaline phosphatase but usually presents with elevated phosphorous levels due to increased bone resorption and altered calcium metabolism.

Thus, the elevation of alkaline phosphatase with normal phosphorous levels aligns well with Paget’s disease as the most likely diagnosis.