NBME 22 Answers : Block 4 : #15 = A 24-year-old woman, gravida 1, para 1, comes to ...

NBME 22 Answers

nbme22/Block 4/Question#15

A 24-year-old woman, gravida 1, para 1, comes to ...

Release of stored thyroid hormone from a thyroid gland infiltrated by lymphocytes

+18 upvote downvote
submitted by liverdietrying(54),

This one was a little tricky. For this one the key is the low radioiodine uptake. This patient has high T4 and low TSH which makes sense in a hyperthyroid patient, perhaps your first thought is that this patient has Grave’s disease. However, in Grave’s your thyroid is being stimulated to make more thyroid hormone from scratch and as such would have an increased radioiodine uptake because the thyroid is bringing in the required (now radiolabeled) iodine. This is why it is not Graves (“release of thyroid hormone from a thyroid stimulated by antibodies”).

So if its not Grave’s what could it be? For this you’d have to know that Hashimoto’s Thyroiditis (also known as Chronic Lymphocytic Thyroiditis and is often referred to as such on board exams to throw you off) has three phases - first they are hyperthyroid, then euthyroid, then the classic hypothyroid that you would expect with low T4 and high TSH. This was the key to this question. The reason for this is that antithyroid peroxidase antibodies in Hashimoto’s cause the thyroid to release all of its stored thyroid hormone making the patient hyperthyroid for a short period of time. After this massive release of thyroid hormone, the antibodies make them unable to make new TH and therefore they become euthyroid for a short period and then hypothyroid which you would expect! Since they can’t make new TH, the thyroid will not take up the radioiodine and therefore there will be low radioiodine uptake. Hence, “release of stored thyroid hormone from a thyroid gland infiltrated by lymphocytes.” aka “Lymphocytic (hashimotos) thyroiditis”.

I think “release of thyroid hormone from a lymphomatous thyroid gland” is referring to some kind of thyroid cancer in which case you would expect them to be describing a nodule on radioiodine uptake.

Summary video here and also a great site in general: https://onlinemeded.org/spa/endocrine/thyroid/acquire

aesalmon pg 338 of FA lists it under hypothyroidism but it does present as transient hyperthyroidism first +4

hyperfukus yep that was the key! Goiter is "HOT" but the remaining answer choices were still kind of bleh D was distracting the hell out of me i spent so long to convince myself to pick C and move on +2

hello Pasting nwinkelmann's comment as an addition: Choice "D" is wrong b/c "lymphomatous thyroid gland" = primary thyroid lymphoma (typically NHL, which is very rare) or Hashimoto's thyroid progression. Hashimoto's thyroiditis = lymphocytic infiltrate with germinal B cells and Hurthle cells, which upon continued stimulation, can lead to mutation/malignant transformation to B cell lymphoma. Both of these present with hypothyroidism with low T4 and high TSH (opposite of this patient). +

taediggity I absolutely love your @liverdietrying, however the pathogenesis of postpartum thyroiditis is similar to Hashimoto's, so I think this person has postpartum thyroiditis and your explanation of transient thyrotoxicosis is spot on, which would also occur in postpartum thyroiditis +3

pg32 I agree with @taediggity. Also note that women eventually recover from postpartum thyroiditis and typically become euthyroid again, which doesn't happen with Hashimoto's. +

vulcania In FA (2019 p. 338) it says that thyroid is usually normal size in postpartum thyroiditis, but the patient in this question had a thyroid "twice the normal size." I guess at the end of the day it doesn't matter which diagnosis is right for this question cause they both seem to lead to the same correct answer :) +1

+11 upvote downvote
submitted by hayayah(603),

This is a patient case of postpartum thyroiditis. Can arise up to a year after delivery and has lymphocytic infiltrate.

almondbreeze FA 2019 pg 338 +1

+1 upvote downvote
submitted by niboonsh(173),

Can someone explain the difference between C. (release of stored thyroid hormone from a thyroid gland infiltrated by lymphocytes) and D. (Release of thyroid hormone from a lymphomatous thyroid gland.

drdoom @niboonsh, ending a comment with a question mark will make it appear on the "comments seeking answers" lists +3

nwinkelmann A lymphomatous thyroid gland can either be due to primary thyroid lymphoma (which is almost always NHL, but is very rare) or due to Hashimoto's thyroid progression. Hashimoto's thyroiditis = lymphocytic infiltrate with germinal B cells and Hurthle cells, which upon continued stimulation, can lead to mutation/malignant transformation to B cell lymphoma. These, I believe, would still present with hypothyroidism, and thus would have low T4 and high TSH (opposite of this patient). +1

+1 upvote downvote
submitted by nwinkelmann(187),

The explanation by liverdietrying plus the explanation in the article posted below (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4989649/) are the best, just need to be combined :). The differential diagnosis table 1 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4989649/table/OM-10-0041-SLTB1/?report=objectonly) specifically identifies the condition in this question as postpartum thyroiditis.

Ultimately, if you know that hypothyroidism has a transient hyperthyroidism phase (due to autoimmune destruction of the cells which already had preformed TH and so it was released upon destruction) before hypothyroidism (nonfunctioning cells so can't take up iodine) and that hypothyroidism is a lymphocytic infiltrating thyroiditis, you will know the answer. I had a hard time understanding this at first because we evaluate/diagnose based on the presence of anti-TPO Ab, but the underlying pathogenesis of the thyroid destruction is cell-mediated (type IV hypersensitivity) not Ab mediated (type II hpyersensitivity) like graves. Hashimoto's = lymphocytic infiltration wiht germinal centers (which can transform to B cell lymphoma) with hurthle cells (pinker cytoplasm cells).

+0 upvote downvote
submitted by seagull(722),

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4989649/

According to this paper, Postpartum Thyroiditis presents with anti-TPO antibodies. The answer choice uses lymphocytes. So this is a transient Hashimotos Hyperthyroidism. Good Luck with that one!

seagull EDIT: Lymphocytes are also present in this as well. My bad +1

+0 upvote downvote
submitted by hyperfukus(43),

I think that since they're asking for an explanation of the patient's current SSx which shows that she's in the state of Transient Hyperthyroidism: which is due to C: Release of stored thyroid hormone from a thyroid gland infiltrated by lymphocytes