Why do I have high BP, lose weight even if I eat and live healthy?

Dear Ask The Doctor: Hello. I am a 20yr old female with a recently high blood pressure and pulse rate. My blood pressure is usually around 90 systolic on 70 diastolic, and my pulse rate similarly low around 60 beats per minute. Of late,my blood pressure is high and my pulse rate at rest is around 100. I also have been experiencing persistent diarrhea, and my metabolism rate is extremely high. I consume a healthy diet, exercise moderately daily, but my BMI is only 17.5. My doctor suspected hyperthyroidism, the thyroid function test were negative. Question:Could you provide me with some differential diagnoses for hyperthyroidism? Thank you.

May I ask what kind of thyroid function test was done? Usually 3 parameters are used to assess thyroid function: TSH, T3 and T4. If all three were normal then further investigations may be needed. Pheochromocytoma (adrenal gland mass) can cause very similar symptoms. Urine and blood tests are needed to diagnose this. Anxiety disorders may have similar manifestations but is usually accompanied by a sense of helplessness. Paroxysmal supraventricular tachycardia will also have an increased heart rate. Rare, but serious causes are metastatic cancer. These are merely differentials; it doesn’t mean you have one of these conditions. Perhaps your doctor will do or is planning to do more tests to determine why you are having unexplained weight loss. I do hope this helps and I wish you well always.