Workup for Purple Striae
The recommended workup for a patient presenting with purple striae should include screening for Cushing syndrome with a 24-hour urinary free cortisol test, late-night salivary cortisol test, or overnight dexamethasone suppression test, as purple striae are a characteristic clinical feature of hypercortisolism. 1, 2
Initial Assessment
When evaluating a patient with purple striae, consider the following:
- Location and appearance: Purple striae, especially when wide and located on the abdomen, are highly suggestive of Cushing syndrome 2, 3
- Associated symptoms: Look for other features of hypercortisolism:
- Facial plethora (redness)
- Central obesity with thin extremities
- Buffalo hump (cervicothoracic fat pad)
- Supraclavicular fat pads
- Proximal muscle weakness
- Facial fullness (moon facies)
- Hypertension
- Easy bruising
- Hirsutism (in females)
Diagnostic Algorithm
Step 1: Rule out exogenous steroid use
- Detailed medication history including topical, inhaled, injected, and oral steroids
- This is the most common cause of Cushing syndrome 2
Step 2: First-line screening tests for Cushing syndrome
Choose at least one of the following:
- 24-hour urinary free cortisol (more than one measurement) 1, 2
- Late-night salivary cortisol (more than one measurement) 2
- 1mg overnight dexamethasone suppression test 2, 4
Step 3: If screening tests are positive
- Measure plasma ACTH levels to determine if Cushing syndrome is ACTH-dependent or independent 2
- Suppressed ACTH: Suggests adrenal cause
- Normal or elevated ACTH: Suggests pituitary or ectopic source
Step 4: Localization studies based on ACTH results
- For ACTH-independent Cushing syndrome: Adrenal imaging (CT or MRI)
- For ACTH-dependent Cushing syndrome: Pituitary MRI and potentially bilateral inferior petrosal sinus sampling 2
Special Considerations
Differential Diagnosis
Purple striae may also be associated with:
- Rapid weight gain or obesity
- Pregnancy
- Adolescent growth spurt
- Marfan syndrome
- Ehlers-Danlos syndrome
Potential Pitfalls
- Pseudo-Cushing states: Conditions like depression, alcoholism, and obesity can cause mild hypercortisolism and should be considered in the differential diagnosis 4
- False positives: Screening tests may be falsely positive in patients with physiologic hypercortisolism 3
- Intermittent hypercortisolism: Some patients may have cyclical Cushing syndrome, requiring repeated testing 3
Pediatric Considerations
In children and adolescents with purple striae, Cushing disease is a common cause of endogenous hypercortisolism. The striae may persist even after successful treatment, though they typically fade from purple to light-colored within the first year after correction of hypercortisolism 5.
Follow-up
- If initial screening tests are negative but clinical suspicion remains high, consider repeating tests or using the dexamethasone-CRH stimulation test 4
- Monitor for comorbidities associated with Cushing syndrome including diabetes, hypertension, and osteoporosis 2
Remember that early diagnosis of Cushing syndrome is crucial as it is associated with significant morbidity and mortality if left untreated 2, 3.