Specificity of Purple Striae for Cushing's Disease
Purple striae (wide purple stretch marks) are highly specific for Cushing's syndrome, though the exact specificity percentage is not quantified in current guidelines—these striae are considered one of the most discriminating clinical features when present. 1, 2
Clinical Significance of Purple Striae
Purple striae represent one of the most specific physical findings for pathologic hypercortisolism, distinguishing it from more common conditions:
Wide purple striae are among the most specific clinical features for Cushing's syndrome, alongside proximal muscle weakness, abnormal fat distribution in supraclavicular and temporal fossae, and decreased linear growth with continued weight gain in children 1
Purple striae are considered a "distinctive clinical feature" that helps differentiate true Cushing's syndrome from pseudo-Cushing's states and simple obesity 3
When hypercortisolism is severe, signs like purple striae make the diagnosis "unmistakable", though not all patients present with every classical feature 2
Important Clinical Context
While purple striae are highly specific when present, several caveats apply:
Many signs and symptoms of Cushing's syndrome are common in the general population (hypertension, weight gain), but purple striae stand out as more discriminating 2
The clinical presentation varies based on the extent and duration of cortisol excess, so purple striae may not be present in all cases, particularly in mild or early disease 2
No single clinical feature has 100% sensitivity, so the absence of purple striae does not exclude Cushing's syndrome—biochemical testing remains essential for diagnosis 4, 5
Practical Application
In clinical practice, the presence of wide purple striae should prompt immediate biochemical screening with late-night salivary cortisol (sensitivity 95%, specificity 100%), 24-hour urinary free cortisol, or dexamethasone suppression testing 5, 6. The combination of purple striae with other specific features (proximal myopathy, supraclavicular fat pads, facial plethora) substantially increases diagnostic certainty and warrants urgent endocrine evaluation 1, 3.