Question

All of the following may be associated with thymoma, except:

• A. SIADH
• B. Myasthenia gravis
• C. Hypogammaglobulinemia
• D. Cushing's syndrome

Hint:

SIADH belongs to small cell lung cancer; thymoma links to myasthenia, Good syndrome, and ectopic ACTH.

Answer 1

The Correct Option is A

Step 1: This is a negative question. Identify the three conditions truly linked with thymoma, and the odd one out is the answer.
Step 2: Myasthenia gravis (option B) is the classic association. About a third of thymoma patients have myasthenia gravis, driven by antibodies against the acetylcholine receptor, and thymectomy can improve the disease. So B is a real association.
Step 3: Hypogammaglobulinemia (option C) is a recognised thymoma association, known as Good syndrome, where thymoma occurs with low immunoglobulins and immunodeficiency. So C is a real association.
Step 4: Cushing's syndrome (option D) can occur with thymoma because some thymic tumours, especially thymic carcinoid type, secrete ACTH and cause ectopic Cushing's syndrome. So D is a real association.
Step 5: SIADH (option A) is the inappropriate secretion of antidiuretic hormone. Its classic tumour link is small cell lung carcinoma, not thymoma. SIADH is not a recognised thymoma association.
Step 6: Therefore the exception is SIADH.
Answer: Option A.