Endocrinology Practice Questions

Q: A 3-week-old female infant presents with ambiguous genitalia and hyperpigmentation of the skin. Laboratory findings include hyponatremia and hyperkalemia. What is the most likely diagnosis?

21 hydroxylase deficiency. **Explanation:** The clinical presentation of ambiguous genitalia in a female infant, skin hyperpigmentation, and electrolyte imbalances (hyponatremia and hyperkalemia) is classic for **Congenital Adrenal Hyperplasia (CAH)**, specifically **21-hydroxylase deficiency**. **1. Why 21-hydroxylase deficiency is correct:** This is the most common cause of CAH (>90%). A deficiency in this enzyme blocks the conversion of progesterone to deoxycorticosterone (mineralocorticoid pathway) and 17-OH progesterone to 11-deoxycortisol (glucocorticoid pathway). * **Mineralocorticoid deficiency:** Leads to "salt-wasting" (hyponatremia, hyperkalemia, and hypotension). * **Glucocorticoid deficiency:** Triggers a feedback increase in ACTH, causing **hyperpigmentation** (due to shared precursor with MSH) and adrenal hyperplasia. * **Androgen excess:** Shunting of precursors toward the androgen pathway causes virilization/ambiguous genitalia in females. **2. Why other options are incorrect:** * **11-beta hydroxylase deficiency:** While it causes virilization and hyperpigmentation, it leads to **hypertension** and hypokalemia because 11-deoxycortisol (which builds up) has mineralocorticoid activity. * **17-alpha hydroxylase deficiency:** This results in decreased sex hormones. Females would have normal external genitalia at birth but fail puberty; males would present with ambiguous genitalia/pseudohermaphroditism. It also causes hypertension. * **17, 20 lyase deficiency:** This affects only sex hormone synthesis. It does not cause salt-wasting or hyperpigmentation as cortisol and aldosterone pathways remain intact. **High-Yield Pearls for NEET-PG:** * **Most common enzyme deficiency:** 21-hydroxylase. * **Diagnostic marker:** Elevated **17-hydroxyprogesterone (17-OHP)**. * **Karyotype:** Usually 46, XX in virilized females. * **Treatment:** Glucocorticoid (Hydrocortisone) and Mineralocorticoid (Fludrocortisone) replacement.

Q: Deep white matter lesion with bilateral deep bright thalamic appearance is suggestive of which condition?

Krabbe's disease. ### Explanation **Krabbe’s Disease (Globoid Cell Leukodystrophy)** The correct answer is **Krabbe’s Disease**. This is an autosomal recessive lysosomal storage disorder caused by a deficiency of the enzyme **Galactocerebrosidase (GALC)**, leading to the accumulation of psychosine, which is toxic to oligodendrocytes. The characteristic neuroimaging finding in the early infantile stage is **hyperdensity (on CT)** or **T2-weighted hypointensity/T1-weighted hyperintensity (on MRI)** in the **thalami**, caudate nuclei, and posterior limb of the internal capsule. This "bright thalamus" appearance, combined with symmetric demyelination of the deep white matter and cerebellar involvement, is a classic diagnostic clue for Krabbe’s. **Analysis of Incorrect Options:** * **Alexander Disease:** Characterized by **frontal lobe predominance** of white matter lesions and "Rosenthal fibers" on pathology. It often presents with macrocephaly. * **Canavan’s Disease:** Notable for **diffuse** white matter involvement including the **subcortical U-fibers** (which are spared in Krabbe’s and MLD) and elevated N-acetylaspartate (NAA) on MR spectroscopy. It also presents with macrocephaly. * **Metachromatic Leukodystrophy (MLD):** Shows a characteristic **"tigroid" or "leopard skin" pattern** of demyelination due to the sparing of perivascular white matter. It typically spares the thalami in early stages. **High-Yield Clinical Pearls for NEET-PG:** * **Krabbe’s:** Look for "Globoid cells" (multinucleated macrophages) on brain biopsy and optic atrophy. * **Macrocephaly + Leukodystrophy:** Think Alexander disease or Canavan’s disease. * **Microcephaly + Leukodystrophy:** Think Krabbe’s disease. * **Tigroid Pattern:** Pathognomonic for MLD (Arylsulfatase A deficiency).

Q: Cretinism is characterized by which of the following physical features?

Disproportionate dwarfism. **Explanation:** **Cretinism** (Congenital Hypothyroidism) results from a deficiency of thyroid hormones during fetal or neonatal life. Thyroid hormone is essential for skeletal maturation and linear growth. In its absence, there is a significant delay in bone age and the maturation of the epiphyseal centers. **Why Option A is Correct:** The hallmark of cretinism is **disproportionate dwarfism**. Thyroid hormone is critical for the growth of long bones. When deficient, the limbs remain short while the trunk continues to grow relatively more, leading to a **low upper segment to lower segment (US:LS) ratio** for the child's age (retaining the infantile proportions where the upper segment is longer). This is distinct from growth hormone deficiency, which typically causes proportionate dwarfism. **Why Other Options are Incorrect:** * **Options B & C:** These descriptions are inaccurate. While the trunk may appear "long" relative to the limbs, the standard clinical terminology is "disproportionate." Short-trunk dwarfism is more characteristic of skeletal dysplasias like Morquio syndrome. * **Option D:** Hypothyroidism leads to growth retardation, not long stature. **Clinical Pearls for NEET-PG:** * **Most common cause:** Thyroid dysgenesis (Ectopic thyroid is the most common specific etiology). * **Early signs:** Prolonged physiological jaundice, poor feeding, constipation, and a large posterior fontanelle (>0.5 cm). * **Classic triad:** Coarse facies, macroglossia (large tongue), and umbilical hernia. * **Radiology:** Absence of the distal femoral epiphysis at birth is a strong indicator of in utero hypothyroidism. * **Treatment:** Levothyroxine (T4) must be started within the first 2 weeks of life to prevent permanent intellectual disability.

Q: Which of the following is a manifestation of 22q11 deletion syndrome?

Conotruncal abnormalities. **Explanation:** **22q11.2 Deletion Syndrome** (which encompasses DiGeorge Syndrome and Velocardiofacial Syndrome) results from a microdeletion leading to the defective development of the **3rd and 4th pharyngeal pouches**. 1. **Why Option B is Correct:** **Conotruncal cardiac abnormalities** are a hallmark of this syndrome, occurring in approximately 75% of patients. These include **Tetralogy of Fallot (most common)**, Interrupted Aortic Arch (Type B), Truncus Arteriosus, and Ventricular Septal Defects. These defects arise due to the failure of neural crest cell migration into the developing outflow tract. 2. **Why the Other Options are Incorrect:** * **A. Hypercalcemia:** Patients actually present with **Hypocalcemia**. This is due to parathyroid hypoplasia (derived from the 3rd/4th pouches), leading to low PTH levels and subsequent tetany or seizures, especially in the neonatal period. * **C. Thymic hyperplasia:** The syndrome is characterized by **Thymic hypoplasia or aplasia**, leading to T-cell deficiency and increased susceptibility to viral and fungal infections. * **D. Dysmorphogenesis of 1st/2nd pouches:** The defect specifically involves the **3rd and 4th pharyngeal pouches**. The 1st and 2nd pouches contribute to the middle ear, tonsils, and tongue, which are not the primary sites of pathology in 22q11 deletion. **High-Yield Clinical Pearls for NEET-PG:** * **CATCH-22 Mnemonic:** **C**ardiac defects, **A**bnormal facies (low-set ears, cleft palate), **T**hymic hypoplasia, **C**left palate, **H**ypocalcemia, **22**q11 deletion. * **Diagnosis:** Gold standard is **FISH** (Fluorescence In Situ Hybridization) or chromosomal microarray. * **Chest X-ray:** Look for the **absence of a thymic shadow** in a neonate.

Question 1

A 3-week-old female infant presents with ambiguous genitalia and hyperpigmentation of the skin. Laboratory findings include hyponatremia and hyperkalemia. What is the most likely diagnosis?

Accepted Answer

21 hydroxylase deficiency

Answer

17 alpha hydroxylase deficiency

Answer

17, 20 lyase deficiency

Answer

11 beta hydroxylase deficiency

Question 2

Deep white matter lesion with bilateral deep bright thalamic appearance is suggestive of which condition?

Accepted Answer

Krabbe's disease

Answer

Alexander disease

Answer

Canavan's disease

Answer

Metachromatic leukodystrophy

Question 3

Cretinism is characterized by which of the following physical features?

Accepted Answer

Disproportionate dwarfism

Answer

Short stature with a long trunk

Answer

Short stature with a short trunk

Answer

Long stature with a long trunk

Question 4

Which of the following is a manifestation of 22q11 deletion syndrome?

Accepted Answer

Conotruncal abnormalities

Answer

Hypercalcemia

Answer

Thymic hyperplasia

Answer

Dysmorphogenesis of the 1st and 2nd pharyngeal pouches

Question 5

What is the least common cause of ambiguous genitalia in a female genotype?

Accepted Answer

Fetal steroid sulphatase deficiency

Answer

21 hydroxylase deficiency

Answer

11 hydroxylase deficiency

Answer

WT1 gene

Endocrinology — MCQs

Endocrinology — MCQs

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