Microphallus Workup

Updated: Nov 30, 2020
  • Author: Karen S Vogt, MD; Chief Editor: Sasigarn A Bowden, MD  more...
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Workup

Laboratory Studies

A karyotype is recommended to confirm chromosomal sex. If PWS is suspected, methylation studies should be performed, and if positive, further genetic analysis for the specific genetic defect is indicated.

Gonadotropins (LH and FSH) reach pubertal levels in healthy male infants, peaking at age 1-3 months and declining by about age 6 months. Excessively high or low values during this "minipuberty" help to narrow the differential diagnoses.

Anti-Müllerian hormone (Müllerian inhibitory substance) and inhibin B are markers of Sertoli cell function and can be useful as indicators of the presence of testicular tissue in the setting of bilateral cryptorchidism.

Testosterone and DHT levels, before and after hCG stimulation, can be measured to evaluate the responsiveness of the testes to gonadotropin stimulation and for 5-alpha reductase deficiency (indicated by an increased testosterone-to-DHT ratio).

Given the possibility of panhypopituitarism, observe all infants with micropenis for hypoglycemia and evidence of other metabolic derangements. If hypoglycemia occurs, obtain a critical sample immediately before intravenous glucose is administered. The critical sample should include glucose, insulin, growth hormone, and cortisol levels.

In infants with hypoglycemia or suspected hypopituitarism, other pituitary hormone function should be evaluated. Evaluation of the thyroid axis should include measurement of total or free thyroxine (T4) as well as thyrotropin stimulating hormone (TSH). Growth hormone and cortisol levels may need to be measured after stimulation (eg, with glucagon for growth hormone and cortisol or ACTH for cortisol).

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Imaging Studies

In situations of genital ambiguity, pelvic ultrasonography is often helpful. The presence of a uterus and ovaries strongly suggests a virilized female (46,XX) infant.

When hypopituitarism is suspected, an MRI scan of the head should be obtained to evaluate the hypothalamic and pituitary areas. In Kallmann syndrome, abnormalities of the olfactory system may be seen.

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Other Tests

Testosterone therapy (testosterone enanthate or cypionate) 25 mg every month for 3 months has diagnostic and therapeutic implications. No appreciable increase in penis size (< 0.9 cm) with androgen therapy suggests androgen insensitivity. [12]

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