Differential Diagnosis for the Newborn
The clinical presentation of this newborn, including female external genitalia with clitoromegaly, bilateral firm masses in the inguinal area, absence of uterus and ovaries on pelvic ultrasonography, and a 46,XY karyotype, suggests a disorder of sex development (DSD). The serum concentrations of luteinizing hormone, follicle-stimulating hormone, estradiol, and testosterone being within the reference ranges help narrow down the differential diagnoses.
Single Most Likely Diagnosis
- Androgen Insensitivity Syndrome (B): This condition is characterized by a 46,XY karyotype, absence or rudimentary development of the uterus and ovaries, and resistance to androgen action, leading to the development of female external genitalia despite the presence of testes (which could be the firm masses felt in the inguinal area). The presence of clitoromegaly might suggest some degree of androgen effect, but this can be seen in partial androgen insensitivity syndrome.
Other Likely Diagnoses
- 5α-reductase Deficiency (D): This condition leads to an inability to convert testosterone to dihydrotestosterone (DHT), which is crucial for the development of male external genitalia. Individuals with this deficiency often have a 46,XY karyotype, testes, and predominantly female external genitalia at birth, with virilization occurring at puberty. The presence of clitoromegaly and the absence of the uterus and ovaries could fit this diagnosis.
- 17β-hydroxysteroid Dehydrogenase 3 Deficiency (E): This enzyme deficiency impairs the conversion of androstenedione to testosterone, leading to undervirilization in 46,XY individuals. They may present with predominantly female external genitalia and testes, which could be consistent with the clinical findings in this case.
Do Not Miss Diagnoses
- 21-hydroxylase Deficiency (F): Although this is the most common cause of congenital adrenal hyperplasia (CAH) and typically presents with virilization in females due to excess androgen production, it's essential to consider it due to the potential for salt-wasting crisis in the neonatal period, which can be life-threatening. However, the clinical presentation and normal serum hormone levels make this less likely.
- Aromatase Deficiency (A): This condition leads to an inability to convert androgens to estrogens, resulting in maternal virilization during pregnancy and potential virilization of a female fetus. In 46,XY individuals, it might not directly explain the female external genitalia but could lead to elevated androgen levels, which are not seen in this case.
Rare Diagnoses
- Kallmann Syndrome (C): This condition is characterized by hypogonadotropic hypogonadism and anosmia. It does not directly explain the female external genitalia in a 46,XY individual and is less likely given the clinical presentation focused on genital ambiguity rather than delayed puberty or hypogonadism.