5 Endocrinology Pearls for the Internal Medicine Shelf and ABIM Board Exam
Endocrinology is an essential part of the Internal Medicine Medical Clerkship and ABIM Board exam. According to the ABIM exam blueprint, questions testing endocrinology topics comprise ~8% of the exam. Approximately ~5-10% of the NBME Clerkship exam is composed of endocrinology questions.
1. Don’t let thyroid nodules intimidate you. Check out the following post ABIM Exam Prep: How to Work Up a Thyroid Nodule This systematic approach will help you workup a thyroid nodule.
2. Workup of hirsutism is not as difficult as it seems. Follow this approach and you will be able to diagnose the cause of hirsutism.
- Hirsutism is caused by either excessive testosterone or excessive 17-OH steroids (DHEA-S) production.
- Excessive Testosterone production is seen in ovarian cancer or polycystic ovarian syndrome (PCOS)
- Ovarian cancer: worked up with trans-vaginal ultrasound to look for adnexal mass. In addition, CA-125 marker is usually elevated in ovarian cancer.
- PCOS: Amenorrhea, insulin resistance, and LH:FSH ratio of greater than equal to 3:1
- Excessive DHEA-S production is seen in congenital adrenal hyperplasia (CAH), Cushing’s disease, or adrenal carcinoma
- CAH: Usual cause is 21 beta hydroxylase deficiency, which is used to convert 17-OH progesterone to cortisol. Since this enzyme is deficient, 17-OH progesterone levels remain elevated. Decreased cortisol levels will cause an elevated ACTH level through a negative feedback mechanism. With increased ACTH, hyperpigmentation will also occur.
- Cushing’s disease: Defect in anterior pituitary causes increased ACTH, which increases cortisol. MRI of pituitary is ordered to work up Cushing’s. If suspicion is high for Cushing’s disease despite negative MRI of the pituitary, perform inferior petrosal sinus sampling.
- Adrenal carcinoma: Problem occurs in the adrenal gland, which will lead to elevated cortisol levels. The elevated cortisol level will suppress the ACTH level. Since ACTH is suppressed, hyperpigmentation will not occur.
- Many times, adrenal masses are found incidentally on a CT scan. These are known as an “adrenal incidentaloma.”
- Rules to remember:
- If the size of the adrenal mass is either greater than 6 cm in size OR is functional (regardless of size) → surgical intervention is recommended
- If an adrenal mass is less than 4 cm AND is non-functional → serial CT scans are recommended every 4-6 months to assess the size of the adrenal mass to make sure it is not growing
- How to determine functional status of an adrenal mass? Remember the 3 layers of the adrenal cortex and the one layer of the adrenal medulla and know what is produced in each layer to determine if it is functioning or not.
- Adrenal Cortex layers (remember by mnemonic GFR as in glomerular filtration rate or GFR):
- Zona Glomerulosa → check to see if aldosterone:renin ratio is elevated (usually more than 20:1)
- Zona Fasiculata → check 24 hour urine cortisol levels and if greater than 100 mg/dl → Cushing problem should be suspected
- Zona Reticularis → Check 17 OH steroid (DHEA-S) levels. If elevated, this layer is functioning.
- Adrenal Medulla: Check urine VMA or urine metanephrine levels. If either of these metabolites are elevated, concern is for pheochromocytoma
- First check 24 hour urine cortisol. If greater than 100 mg/dl, then you either have Cushing syndrome, Cushing disease, or ectopic production of ACTH.
- Next step is to check ACTH level. If ACTH level is suppressed, then the problem is Cushing syndrome, CT or MRI of adrenals should be done. If ACTH level is elevated, the patient has either Cushing’s disease (pituitary problem) or ectopic production of ACTH (like lung cancer)
- To distinguish between Cushing’s disease and ectopic production of ACTH, perform a high dexamethasone suppression test (8 mg).
- If high dose dexamethasone suppresses cortisol, problem is Cushing’s disease. MRI of the pituitary should be performed. If MRI of the pituitary is negative, perform inferior petrosal sinus sampling.
- If high dose dexamethasone suppression test fails to suppress cortisol, the problem is ectopic production of ACTH. Check CT scan of chest to rule out lung cancer.
- Type 1 DM → lack of insulin because of destruction of pancreatic beta cells → associated with antibodies to glutamic acid decarboxylase
- Type 2 DM → more common in obese individuals and can occur later in life. Insulin resistance occurs.
- Diagnose of DM is made when patient has two fasting glucose levels greater than or equal to 126 mg/dl or a random glucose level greater than 200 mg/dl.
- Goal Hgba1C is less than 7%. Hgba1C is an average glucose in a 3 month period.
- Pre-prandial glucose goal in a DM patient is 90-130 mg/dl. 2 hour post-prandial glucose goal is less than 180 mg/dl.
- Monofilament foot testing is the best way to prevent diabetic foot ulcers from occurring. A common organism that causes diabetic foot ulcers is Staph aureus or beta hemolytic streptococcus.
- Goal Blood pressure in a DM patient is less than 130/80 → anti-hypertensive of choice to achieve this blood pressure is either an ACE inhibitor or an ARB.
- Eye exams in DM patients are recommended on a yearly basis
- If eye exam reveals hard exudates or microaneurysms → patient has non-proliferative retinopathy → management is by tighter glucose control
- If eye exam reveals neovascularization or cotton-wool spots → patient has proliferative retinopathy → treat with photocoagulation
Once again, the folks who write the Internal Medicine licensing exams don’t expect you to have the depth of knowledge regarding hormone-related conditions, metabolism and diabetes conditions that an endocrinologist possesses. However, topics such as the ones mentioned in the pearls above should assist you with the endocrinology section of the med school clerkship shelf and ABIM board exams.