Dermatological Signs and Phenomena
On this page
Direct answer
Dermatological signs and phenomena are bedside findings elicited by a simple manoeuvre, such as scraping, rubbing or applying pressure, that point to a specific diagnosis. The Auspitz sign, pinpoint bleeding after removing a scale, is characteristic of psoriasis. The Nikolsky sign, sliding of the epidermis under lateral pressure, is positive in pemphigus vulgaris, toxic epidermal necrolysis and staphylococcal scalded skin syndrome.
What you must remember
- Auspitz sign: pinpoint bleeding from the papillary capillaries after removing a psoriatic scale, seen in psoriasis.
- Koebner phenomenon: the isomorphic response, in which new lesions appear at sites of trauma, seen in psoriasis, lichen planus, vitiligo and warts.
- Nikolsky sign: the epidermis slides off or separates under lateral pressure, positive in pemphigus vulgaris, staphylococcal scalded skin syndrome and toxic epidermal necrolysis.
- Asboe-Hansen sign: an intact bulla spreads sideways when vertical pressure is applied to its roof, seen in the pemphigus group and toxic epidermal necrolysis.
- Darier sign: stroking a lesion of urticaria pigmentosa produces a wheal, because of mast cell degranulation.
- Wickham striae: fine white lacy lines on the surface of lichen planus papules and oral lesions.
- Pastia lines: linear, deep red accentuation of skin creases in the flexures, characteristic of scarlet fever.
A bedside sequence for eliciting the signs
Most of these signs need only a clinician's finger, a glass slide or a blunt instrument, so they can be checked during the first examination. The order matters, because Asboe-Hansen testing needs an intact bulla that Nikolsky testing might rupture.
- Inspect the surface: note scale, erosions and bullae before touching the lesion.
- Scrape the scale: use a glass slide or blunt edge to remove psoriatic scale and look for the Auspitz sign.
- Apply lateral pressure: slide a finger across apparently normal or eroded skin to test for the Nikolsky sign.
- Press an intact bulla: apply vertical pressure to its roof and watch for lateral spread, which is the Asboe-Hansen sign.
- Stroke a papule: stroke a lesion of urticaria pigmentosa to see whether it wheals, which is the Darier sign.
- Check for trauma-induced lesions: look for new lesions along scratch or scar lines, which indicates the Koebner phenomenon.
Positive findings narrow the differential, but they do not replace histology, so a biopsy is still needed to confirm the diagnosis.
Where sign questions split candidates
Eponymous signs are easy to memorise and easy to confuse, so examiners often set traps between similar names.
- Trap: confusing the Darier sign with Darier disease Correct: the Darier sign is a wheal on stroking urticaria pigmentosa, whereas Darier disease is a genetic disorder of keratinisation caused by ATP2A2 mutations.
- Trap: treating a positive Nikolsky sign as proof of pemphigus alone Correct: it is also positive in staphylococcal scalded skin syndrome and toxic epidermal necrolysis, so histology and the clinical setting are needed.
- Trap: assuming the Koebner phenomenon proves psoriasis Correct: it occurs in lichen planus, vitiligo and warts too, so it shows trauma-induced spread rather than the diagnosis.
- Trap: linking Pastia lines to measles Correct: Pastia lines are accentuated flexural creases that accompany the rash of scarlet fever.
Frequently asked questions
Which sign is positive in pemphigus vulgaris and toxic epidermal necrolysis?
The Nikolsky sign is positive in pemphigus vulgaris and toxic epidermal necrolysis, and also in staphylococcal scalded skin syndrome. It is elicited by applying lateral pressure to the skin, which causes the epidermis to slide off the dermis.
What does the Darier sign indicate in urticaria pigmentosa?
The Darier sign is a wheal that forms when a lesion of urticaria pigmentosa is stroked, reflecting mast cell degranulation in the lesion. It should not be confused with Darier disease, which is an inherited disorder of keratinisation.
How is the Auspitz sign elicited and which disease shows it?
The Auspitz sign is elicited by scraping psoriatic scale with a glass slide, which produces pinpoint bleeding from the dilated papillary capillaries. It is characteristic of psoriasis, although it is not a reliable stand-alone finding.
Why does the Koebner phenomenon matter in psoriasis?
The Koebner phenomenon is the appearance of new lesions at sites of skin trauma, such as scratches, scars or friction. Psoriasis, lichen planus, vitiligo and warts all show it, so susceptible patients should avoid skin injury such as tattooing and needless surgery.
Which sign is typical of scarlet fever?
Pastia lines are linear, deep red accentuations of skin creases, most often in the axillae, antecubital fossae and groin. They accompany the rash of scarlet fever, and they help distinguish it from other exanthems in examination questions.