A 55 year old man, a chronic smoker is brought to emergency with history of polyuria, polydipsia, nausea and altered sensorium for last two days. He had been diagnosed as having squamous cell carcinoma of lung two months prior to this. On examination, he was lethargic and confused. An ECG was normal except for a narrowed QT interval. Which one of the following is the most likely metabolic abnormality ?

**Core Concept**
Hypercalcemia is a common metabolic complication in malignancy, especially in squamous cell carcinoma of the lung, due to the secretion of parathyroid hormone-related protein (PTHrP) by tumor cells. This leads to increased bone resorption, elevated serum calcium, and neuromuscular irritability, which can manifest as confusion, lethargy, and altered sensorium.

**Why the Correct Answer is Right**
Squamous cell carcinoma of the lung is known to secrete PTHrP, which mimics parathyroid hormone and stimulates osteoclast activity, resulting in hypercalcemia. The clinical presentation of polyuria, polydipsia, nausea, and altered sensorium aligns with hypercalcemia-induced CNS effects. The narrowed QT interval on ECG is a classic ECG finding in hypercalcemia due to decreased cardiac repolarization. This triad—malignancy, symptoms, and ECG change—strongly supports hypercalcemia as the underlying metabolic abnormality.

**Why Each Wrong Option is Incorrect**
Option A: Hypotremia is not a recognized metabolic abnormality; it is a misstatement of hypotension, which is not linked to this clinical picture.
Option C: Hypokalemia typically causes muscle weakness, arrhythmias, and constipation, not altered sensorium or polyuria. It does not explain the ECG change or clinical symptoms.
Option D: Hyponatremia causes confusion and seizures, but it presents with headache, seizures, and neurologic deterioration, not polyuria or polydipsia. It is also not commonly associated with lung cancer.

**Clinical Pearl / High-Yield Fact**
Lung cancer, especially squamous cell carcinoma, is a leading cause of hypercalcemia due to PTHrP secretion. Always consider hypercalcemia in any patient with malignancy presenting with altered mental status and polyuria—early recognition is critical for treatment.

✓ Correct Answer: B. Hypercalcemia

✓ Correct Answer: B. Hypercalcemia