Thread by @mendesthiagob

Hey #MedTwitter,

In endocrinology, the concept of "inappropriately normal" is the basis for the interpretation of several labs results.

Do you understand this concept? It is definitely one of the most important for understanding endocrine diseases.

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📢 Clinically, it means the problem is not with the hormone itself. It means the problem is with the "hormone coordinator", which may sound normal when it is actually failing to respond as it should.

Let's clarify it!

With few exceptions, hormones control their own secretion by a mechanism called "negative feedback".

Let's use an example:
- Thyroid secretes T3/T4 controlled by TSH.
- T3/T4 act in the pituitary controlling TSH secretion.
--> T3/T4 negatively impact TSH secretion

What to expect if the thyroid produces fewer hormones?
- 1) Less T3/T4 will act in the pituitary
- 2) Pituitary will "read" it and produce more TSH in the attempt to stimulate the thyroid.

What if there is ⬇️ T3/T4 and TSH is normal?

It means the feedback is not working.

It means the problem is not in the thyroid itself.

⬇️ thyroid hormones and normal TSH = inappropriately normal TSH, meaning the problem is in TSH secretion (pituitary, hypothalamus)

⬇️ cortisol and normal ACTH = inappropriately normal ACTH = secondary adrenal insufficiency

⬇️ calcium and normal PTH = inappropriately normal PTH = primary hypoparathyroidism

⬇️ glucose and normal insulin = inappropriately normal insulin = insulin-dependent hypoglycemia

This is what "inappropriately normal" is about!

If it is "inappropriately normal", you know where the problem is!

👊👊