HY lecture notes:
Hypothyroidism at 2CK level won’t go the whole “constipation, brittle hair, dry skin” route; instead they’ll tell mention things like:
- Low mood (anyone, particularly over 50, who is dysthmic –> do a TSH)
- Bradycardia (low HR can by all means be normal, but you’ll notice they’ll say the HR is 55-60 in hypothyroidism Qs)
- Proximal muscle weakness (hypothyroid myopathy –> thyroid hormone necessary for mitochondrial function –> loss of type II muscle fibers over time); increased serum creatine kinase is HY
- High cholesterol
- High hepatic ALT and AST (weird, but it shows up on the 2CK NBME forms)
- From source: “An increase in the aspartate aminotransferase (AST) and alanine aminotransferase (ALT) was reported in 27% and 37% of patients respectively, although the majority of these patients showed no other clinical or biochemical features of liver impairment. The mechanism of injury appears to be relative hypoxia in the perivenular regions, due to an increase in hepatic oxygen demand without an appropriate increase in hepatic blood flow.”
- Periods increasing in duration and heaviness
For pregnancy, evaluate thyroid with free T4, not TSH.
Increased estrogen –> increased thryoid-binding globulin (TBG) production by liver –> mops up free T4 (active form of T4) –> transient decrease in free T4 (total T4 still the same) –> TSH increases to compensate –> thyroid gland produces more T4 (total T4 is now high + free T4 restored) –> TSH goes back to normal –> Bottom line, in pregnancy: normal TSH, normal free T4, high total T4, high TBG due to high estrogen.
Peds form will ask the inverse: kid has normal free T4 but decreased total T4 –> answer = thyroid-binding globulin deficiency. If you understand the pregnancy concept, then this makes sense.
GnRH abnormal pulsation seen in both amenorrhea due to anorexia, as well in anovulation/PCOS due to insulin resistance, although the mechanisms are entirely different.
In PCOS:
Cause USMLE wants for anovulation / PCOS –> insulin resistance –> that’s why usually seen in high BMI.
Insulin resistance causes abnormal GnRH pulsation –> abnormal GnRH pulsation causes high LH/FSH ratio –> high LH means hirsutism; low FSH means follicles aren’t adequately primed by the time the LH spike occurs to signal ovulation –> anovulation
Why high LH/FSH ratio important in anovulation/PCOS –> once again, ovulation is stimulated when follicle not ready –> no ovulation (anovulation) –> follicle retained as cyst
In anorexia:
Low adipose –> less peripheral aromatization of androgens to estrogens –> less GnRH pulsation, period –> low FSH and low LH –> amenorrhea due to mere reduction of gonadotropins + follicles do not mature the way they do in PCOS. Patients with amenorrhea due to anorexia technically do not ovulate, but the term “anovulation” used on its own implies an insulin resistance mechanism on the same spectrum as PCOS (discussed more in lecture #8).
Hematocolpos –> pooled blood in the vagina usually due to an imperforate hymen –> bluish bulge seen behind the hymen on physical exam –> can present with cyclical abdominal pain/cramping because the girl is still having her periods but the blood is merely trapped –> Tx = cruciate incision of the hymen.
Hematometra –> pooled blood behind the cervix (in the uterus) due to imperforate hymen (blood backs up further) or conditions like congenital transverse vaginal septum –> uterus can sometimes be palpable on physical exam + patient may have low BP (literature says this may be due to accumulation of blood in the uterus precipitating a vasovagal response). Tx = cruciate incision of the hymen (answer on USMLE); if due to a cervical problem, can do cervical dilatation.
