What is the initial evaluation and treatment approach for a patient presenting with micropenis, considering their medical history, physical examination, and potential underlying hormonal imbalances?

Evaluation and Management of Micropenis

Begin evaluation by measuring stretched penile length (SPL) using standardized technique and comparing to age-appropriate normative data—micropenis is defined as SPL >2.5 standard deviations below the mean for age, which translates to <2 cm at birth or <4 cm after age 5 years. 1

Initial Diagnostic Evaluation

Physical Examination

• Measure stretched penile length using standardized technique with the penis stretched along its dorsal surface to maximum length without causing discomfort, measured from pubic symphysis to tip of glans 2, 1
• Differentiate true micropenis from buried/hidden penis or aphallia—micropenis has normal penile structure but abnormally small size 2
• Examine for associated genital anomalies including hypospadias, incomplete scrotal fusion, and cryptorchidism, as these suggest disorders of sex development (DSD) 1
• Assess testicular size and position to evaluate for gonadal dysgenesis or testicular regression 1
• Perform ultrasound of genitalia to assess for associated structural abnormalities 3

Essential History Components

• Document growth velocity carefully—poor growth suggests associated hypothalamic or pituitary pathology 2
• Identify syndromic features suggestive of hypogonadotropic hypogonadism (Kallmann syndrome, CHARGE syndrome, Prader-Willi syndrome) 2
• Obtain detailed family history of consanguinity, genital abnormalities, or infertility 1

Laboratory Investigation

Hormonal Assessment

• Measure basal gonadotropins (LH, FSH) and testosterone levels as initial screening 1
• Perform human chorionic gonadotropin (hCG) stimulation test to assess testicular function—measure testosterone, dihydrotestosterone (DHT), and androstenedione at baseline and after stimulation 2, 1
• Consider GnRH stimulation test to differentiate hypothalamic from pituitary causes of hypogonadotropic hypogonadism 2

Genetic Testing

• Obtain karyotype analysis in all patients, particularly when associated DSD features are present 1
• Consider additional genetic testing for specific syndromes when clinically indicated 1

Etiologic Classification

The underlying causes fall into four main categories:

• Hypogonadotropic hypogonadism (hypothalamic or pituitary failure)—most common endocrine cause 2
• Hypergonadotropic hypogonadism (primary testicular failure, partial gonadal dysgenesis, testicular regression) 2, 1
• Partial androgen insensitivity syndrome (disorders of testosterone biosynthesis or androgen receptor action) 2, 1
• Idiopathic micropenis (no identifiable cause) 2

Treatment Approach

Hormonal Therapy: First-Line Treatment

All patients with micropenis should receive a trial of testosterone therapy regardless of underlying etiology, as this demonstrates the penis's capacity to respond to androgens and guides further management. 2

Treatment Protocols by Age

For infants and children <11 years:

• Administer intramuscular testosterone enanthate 25 mg once monthly for 3 months 4
• Alternative: Apply topical testosterone or DHT gel to the penis in the neonatal or infancy period 1
• Expected response: Penile length increases from mean 15.5 mm to 37.2 mm (P<0.001) 4

For children >11 years (prepubertal/early pubertal):

• Administer human chorionic gonadotropin 1,500-2,000 IU intramuscularly once weekly for 6 weeks 4
• Expected response: Testosterone levels increase from <20 ng/mL to 449 ng/mL, and penile length increases from mean 26.4 mm to 64.3 mm (P<0.001) 4

For pubertal-age patients:

• Begin with one or two short courses of testosterone enanthate (25-50 mg intramuscularly every 4 weeks for 3 injections) 5
• At pubertal age, gradually increase dose to 200 mg monthly, then advance to adult replacement regimen 5
• Expected adult outcome: Mean final penile length of 10.3 cm (range 8-14 cm), which is within 2 SD of normal adult mean of 12.4 cm 5

Critical Treatment Principles

• Initiate hormonal therapy in infancy or early childhood when possible—early treatment (before age 2 years) produces comparable adult penile length to treatment started at ages 6-13 years 5
• Reassess penile response after each treatment course to determine need for additional therapy 2
• For patients with growth hormone deficiency and hypopituitarism, provide appropriate hormonal replacement therapy as these patients respond well to combined treatment 2

Surgical Management: Rarely Indicated

Surgical correction is NOT indicated for common endocrine types of micropenis and should be reserved only for patients who fail hormonal therapy and have realistic expectations about outcomes 2, 6

• Total phalloplasty using radial-artery-based forearm flaps can restore normal penile length but carries significantly higher complication rates 6
• Conservative surgical techniques (length or girth enhancement) provide minimal improvement with lower complication rates 6
• Sex reassignment is performed very infrequently now given that testosterone-treated children achieve satisfactory penile length and sexual function 2, 5

Long-Term Outcomes and Counseling

• Most testosterone-treated patients achieve normal male gender identity, psychosocial behavior, and sexual function—6 of 8 men in one study were sexually active as adults 5
• Testosterone treatment in infancy or childhood does NOT impair subsequent penile growth during adolescence or compromise adult penile length 5
• Patients with penile dysmorphic disorder require intensive psychological counseling before considering any surgical intervention 6

Key Clinical Pitfalls to Avoid

• Do not diagnose micropenis without using standardized measurement technique and age-appropriate normograms—buried penis is frequently misdiagnosed as micropenis 2, 1
• Do not recommend sex reassignment without attempting hormonal therapy first—there are no clinical, psychological, or physiological indications to support conversion of affected male infants to females 5
• Do not delay evaluation in children >1 year of age with SPL <1.9 cm—early diagnosis and treatment optimize outcomes 2
• Do not pursue surgical correction as first-line therapy—hormonal treatment produces satisfactory results in most patients 2