Mechanism of Auspitz Sign in Psoriasis
The Auspitz sign in psoriasis is primarily caused by parakeratosis, which leads to the appearance of small bleeding points when scales are removed from psoriatic lesions.
Understanding the Auspitz Sign
The Auspitz sign refers to the appearance of small bleeding points after successive layers of scale have been removed from the surface of psoriatic papules or plaques. This clinical sign has traditionally been associated with psoriasis, though research shows it has limitations in both sensitivity and specificity.
Pathophysiological Mechanism
The mechanism behind the Auspitz sign involves several histopathological features of psoriasis:
Parakeratosis - This is the primary mechanism responsible for the Auspitz sign 1:
- Parakeratosis refers to the retention of nuclei in the stratum corneum
- In psoriasis, there is incomplete keratinization with persistent nuclei in the outer epidermal layer
- This creates a less cohesive scale that separates more easily when scraped
Contributing factors:
Clinical Significance and Limitations
Research has shown that the Auspitz sign has important limitations:
- Sensitivity: The Auspitz sign was present in only 41 of 234 patients (17.5%) with confirmed psoriasis in one study 2
- Specificity: Small bleeding points can also be produced when scale is forcibly removed from other scaling disorders, including Darier's disease and actinic keratoses 2
Diagnostic Value
Despite its limitations, the Auspitz sign can still contribute to diagnosis when considered alongside other clinical features:
- When present alongside typical silvery white scale and Koebner's phenomenon, it increases diagnostic accuracy for psoriasis 1
- In the absence of these clinical signs, histological evidence of suprapapillary thinning and absent granular layer may help confirm the diagnosis 1
Clinical Application
When examining a patient with suspected psoriasis:
- Look for well-defined erythematous plaques with silvery scales
- Gently scrape the surface of the lesion with a glass slide or curette
- Observe for pinpoint bleeding (Auspitz sign)
- Remember that while a positive Auspitz sign supports a diagnosis of psoriasis, its absence does not rule it out
- Consider histopathological confirmation in ambiguous cases
The Auspitz sign remains a useful clinical tool when interpreted in the appropriate context, but clinicians should be aware of its limitations and consider the complete clinical picture when making a diagnosis of psoriasis.