A 65 years old male diagnosed by biopsy a case of lung carcinoma, with paraneoplastic syndrome and increased PTH. Probable cause is-
**Core Concept**
Lung carcinoma can cause paraneoplastic syndromes, which are remote, nonmetastatic effects of cancer on distant tissues and organs. In this case, the patient has increased PTH, indicating hyperparathyroidism, a paraneoplastic syndrome associated with certain types of cancer.
**Why the Correct Answer is Right**
The most common cause of paraneoplastic hyperparathyroidism is squamous cell lung carcinoma, which secretes parathyroid hormone-related protein (PTHrP). This protein mimics the action of PTH, leading to hypercalcemia and increased PTH levels. The PTHrP binds to the PTH receptors on the parathyroid glands, suppressing the production of PTH, and on the bones, kidneys, and intestines, promoting calcium resorption, reabsorption, and absorption, respectively.
**Why Each Wrong Option is Incorrect**
**Option A:** This is not a known cause of paraneoplastic hyperparathyroidism.
**Option B:** While certain lung cancers can cause paraneoplastic syndromes, this is not the most common cause of paraneoplastic hyperparathyroidism.
**Option D:** This is not a known cause of paraneoplastic hyperparathyroidism.
**Clinical Pearl / High-Yield Fact**
Squamous cell lung carcinoma is the most common cause of paraneoplastic hyperparathyroidism, and the diagnosis is often made by measuring PTHrP levels.
**Correct Answer:** C. Squamous cell lung carcinoma.