In an adolescent with atypical shoulder and lateral abdominal striae, what is the most appropriate next step to determine if they represent Cushing syndrome rather than physiologic adolescent striae?

Evaluating Atypical Striae in Adolescents for Cushing Syndrome

In an adolescent with atypical shoulder and lateral abdominal striae, screen for Cushing syndrome only if the striae are accompanied by unexplained weight gain combined with either growth deceleration or a decline in height velocity. 1

Key Clinical Discriminators

The presence of growth failure (declining height velocity or height standard deviation score) combined with weight gain has high sensitivity and specificity for distinguishing pathologic Cushing syndrome from physiologic adolescent striae in prepubertal children and young adolescents. 1 This combination is the most reliable clinical indicator that warrants biochemical investigation.

Clinical Features That Suggest Pathologic Cushing Syndrome

Beyond the growth pattern, look for these specific features that distinguish Cushing syndrome from normal adolescent changes:

• Wide (>1 cm), reddish-purple striae rather than thin, pink striae 2, 3
• Facial plethora (persistent facial redness) 2, 4
• Proximal muscle weakness (difficulty rising from a chair or climbing stairs) 4, 3
• Easy bruising without significant trauma 4, 3
• Supraclavicular or dorsocervical fat pads 2

Important caveat: Post-pubertal adolescents cannot be reliably assessed using growth parameters alone, as linear growth may be complete. These patients require assessment according to adult guidelines focusing on the discriminatory features listed above. 1

When NOT to Pursue Testing

Do not screen for Cushing syndrome in adolescents with:

• Striae alone without growth deceleration 1
• Simple obesity with normal or accelerated growth velocity 1
• Isolated weight gain without declining height percentiles 1

The vast majority of obese adolescents do not have Cushing syndrome, and few patients with obesity prove to have the condition. 1

Biochemical Screening Algorithm (If Clinical Criteria Met)

If the adolescent meets screening criteria (unexplained weight gain + growth deceleration), proceed with first-line biochemical testing using any one of these three tests 1:

1. 24-hour urinary free cortisol (UFC) - collect for 3 consecutive days

   • Diagnostic threshold: >193 nmol/24h (>70 μg/m²)
   • Sensitivity: 89%, Specificity: 100% 1

2. Late-night salivary cortisol

   • Based on local assay cut-off
   • Sensitivity: 95%, Specificity: 100% 1

3. Low-dose dexamethasone suppression test (LDDST)

   • Dose: 0.5 mg every 6 hours for 48 hours (or 30 μg/kg/day if <40 kg)
   • Failure to suppress cortisol to <50 nmol/L indicates Cushing syndrome
   • Sensitivity: 95%, Specificity: 80% 1

Critical point: None of these tests has 100% diagnostic accuracy, and each has limitations. 1 First, eliminate exogenous glucocorticoid use before any biochemical testing. 1

Common Pitfalls to Avoid

• Do not rely on random cortisol measurements - they are unreliable for screening 4
• Do not screen based on striae appearance alone - physiologic adolescent striae are extremely common and do not warrant investigation without accompanying growth failure 1
• Do not overlook medication interference - drugs affecting CYP3A4 metabolism can cause false-positive or false-negative results on dexamethasone suppression testing 1
• Ensure complete 24-hour urine collections - incomplete collections are a major source of false-negative UFC results 1, 5