MRCP2-3364

MRCP2-3364

A 14-year-old male presents to your clinic with complaints of increasing fatigue at school over the past 2 months. His parents are worried that he relies on large amounts of Lucozade to stay alert during his secondary school exams. He denies any headaches. The patient had a normal pregnancy and development until he was 12 years old when he underwent chemotherapy and radiotherapy for an optic chiasm glioma, causing him to miss a year of school. He returned to school after treatment and has been achieving good grades. There is no significant past medical or family history.

Upon examination, the patient is short for his age (at 2nd centile) and lacks facial hair or other secondary sexual characteristics. He has a BMI of 13.7 kg/m² and appears thin. Chest, cardiovascular, and abdominal examinations are unremarkable, and there are no skin lesions. Neurological examination, including cranial nerves, is normal.

The initial blood tests reveal the following results:

Hb 142 g/l
MCV 89 fl
Platelets 410 * 109/l
WBC 7.4 * 109/l
Na+ 139 mmol/l
K+ 4.6 mmol/l
Urea 5.1 mmol/l
Creatinine 44µmol/l
FSH low
ACTH low
TSH 0.13 mu/l

What is the most likely diagnosis?