A 45-year-old woman with severe asthma has been on oral prednisolone 20 mg daily for 8 months. On examination, she has a prominent dorsocervical fat pad (marked **C** in the diagram), along with moon facies, central obesity, and proximal muscle weakness. Which of the following best explains the pathophysiology of the structure marked **C**?

Explanation

## Why "Abnormal fat redistribution to the dorsal neck due to glucocorticoid excess and altered lipolysis" is right The structure marked **C** — the buffalo hump or dorsocervical fat pad — is a classic feature of Cushing syndrome caused by abnormal fat redistribution secondary to glucocorticoid excess. Glucocorticoids promote lipolysis in the extremities while simultaneously enhancing lipogenesis and fat deposition in the trunk, neck, and face. This patient's 8-month exposure to high-dose prednisolone (20 mg daily) has induced iatrogenic Cushing syndrome, the most common cause of Cushing phenotype. The dorsocervical fat pad, combined with moon facies and central obesity, forms part of the characteristic cushingoid appearance. Per Robbins 10e Ch 24 and Harrison 21e Ch 386, this abnormal fat redistribution is a hallmark of glucocorticoid excess. ## Why each distractor is wrong - **Lipohypertrophy from chronic insulin administration**: This patient is on prednisolone, not insulin. Lipohypertrophy occurs at insulin injection sites and is not a feature of Cushing syndrome. The clinical presentation (moon facies, central obesity, proximal weakness) is consistent with glucocorticoid excess, not diabetes management. - **Thyroid enlargement secondary to iodine deficiency and hypothyroidism**: While chronic glucocorticoids can suppress TSH and cause secondary hypothyroidism, thyroid enlargement is not a feature of Cushing syndrome. The dorsocervical swelling in this case is fat, not thyroid tissue. Hypothyroidism would not explain the moon facies, central obesity, or proximal weakness. - **Lymphadenopathy from opportunistic infection**: Although immunosuppression is a recognized complication of chronic glucocorticoid use (requiring PCP prophylaxis with high-dose/long-term steroids), lymphadenopathy is not the primary cause of the dorsocervical fat pad. The clinical picture is dominated by cushingoid features, not infection. **High-Yield:** Buffalo hump = dorsocervical fat pad = abnormal glucocorticoid-driven fat redistribution; combined with moon facies + central obesity + proximal weakness = classic iatrogenic Cushing syndrome (most common cause of Cushing phenotype). [cite: Robbins 10e Ch 24; Harrison 21e Ch 386]