Endocrinology — MCQs
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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?
Deep white matter lesion with bilateral deep bright thalamic appearance is suggestive of which condition?
Cretinism is characterized by which of the following physical features?
Which of the following is a manifestation of 22q11 deletion syndrome?
What is the least common cause of ambiguous genitalia in a female genotype?
Endocrinology Indian Medical PG Practice Questions and MCQs
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?
- A. 21 hydroxylase deficiency (Correct Answer)
- B. 17 alpha hydroxylase deficiency
- C. 17, 20 lyase deficiency
- D. 11 beta hydroxylase deficiency
Explanation: **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.
Question 2: Deep white matter lesion with bilateral deep bright thalamic appearance is suggestive of which condition?
- A. Alexander disease
- B. Canavan's disease
- C. Krabbe's disease (Correct Answer)
- D. Metachromatic leukodystrophy
Explanation: ### 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).
Question 3: Cretinism is characterized by which of the following physical features?
- A. Disproportionate dwarfism (Correct Answer)
- B. Short stature with a long trunk
- C. Short stature with a short trunk
- D. Long stature with a long trunk
Explanation: **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.
Question 4: Which of the following is a manifestation of 22q11 deletion syndrome?
- A. Hypercalcemia
- B. Conotruncal abnormalities (Correct Answer)
- C. Thymic hyperplasia
- D. Dysmorphogenesis of the 1st and 2nd pharyngeal pouches
Explanation: **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 5: What is the least common cause of ambiguous genitalia in a female genotype?
- A. 21 hydroxylase deficiency
- B. 11 hydroxylase deficiency
- C. Fetal steroid sulphatase deficiency (Correct Answer)
- D. WT1 gene
Explanation: **Explanation:** Ambiguous genitalia in a female genotype (46,XX) is most commonly caused by **Female Pseudohermaphroditism**, where an excess of androgens leads to virilization of a genetically female fetus. **Why Option C is correct:** **Fetal Steroid Sulphatase Deficiency** (also known as Placental Sulphatase Deficiency) is associated with **X-linked Ichthyosis**. In this condition, the placenta cannot convert DHEAS into estriol. This leads to extremely low maternal serum estriol levels and failure of labor induction. Crucially, it **does not** cause virilization or ambiguous genitalia in the female fetus. In fact, it is a condition primarily affecting male fetuses (X-linked), making it the "least common" (or non-existent) cause among the choices provided. **Analysis of Incorrect Options:** * **A. 21-Hydroxylase Deficiency:** This is the **most common** cause of ambiguous genitalia in 46,XX (responsible for ~90% of Congenital Adrenal Hyperplasia cases). It causes a "salt-wasting" or "simple virilizing" crisis due to shunting of precursors to androgens. * **B. 11-Beta-Hydroxylase Deficiency:** The second most common cause of CAH. It causes virilization in females and is uniquely associated with **hypertension** due to the accumulation of 11-deoxycorticosterone (DOC). * **D. WT1 Gene Mutations:** Mutations in the Wilms Tumor 1 gene (e.g., Denys-Drash or Frasier Syndrome) typically cause 46,XY gonadal dysgenesis, but they are recognized causes of complex disorders of sexual development (DSD) and can present with ambiguous genitalia. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of 46,XX DSD:** Congenital Adrenal Hyperplasia (21-OH deficiency). * **Maternal cause of female virilization:** Luteoma of pregnancy or intake of androgenic progestins. * **Prader Staging:** Used to describe the degree of virilization of external genitalia in females. * **Steroid Sulphatase Deficiency Key Clue:** "Low estriol in a pregnant female with a post-dated pregnancy and fish-scale skin (ichthyosis) in the male newborn."
Practice by Chapter
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