At the dermatologic examination, several simple bedside tests may help to narrow the differential diagnosis. The most commonly performed bedside tests are listed below. For functional and imaging tests dermatopathology and other tests see chapters 9.2.2 - 9.2.4.
9.2.1 Bedside Tests
Nikolsky sign is shearing away the epidermis after gentle lateral or tangential pressure or rubbing the peri-bullous skin. It is positive in patients with pemphigus, staphylococcal scalded skin syndrome (SSSS), and toxic epidermal necrolysis (Lyell's disease).
Indirect Nikolsky (Nikolsky II) is elicited by the gentle pressure on an intact bulla that results in the spread of fluid in the epidermis away from the site of pressure (the “bulla-spread phenomenon”).
Darier sign designates the rapid appearance of a wheal or an acute or late persisting erythema when the lesion is stroked. It typically occurs in patients with cutaneous mastocytosis or urticaria factitia
Auspitz sign is the appearance of punctate bleeding after removing the scales from plaques in psoriasis. The erythematosquamous plaque is gently scraped with a tongue depressor or a glass slide, resulting in the removal of silvery scales. After scraping off all the scales, a glistening transparent membrane (Buckley's membrane) appears. On removing the membrane, punctate bleeding points are observed. Bleeding comes from the capillaries of the papillary layer beneath a thinner epidermis between broad rete ridges.
Skin scraping for diagnosing fungal infections and scabies
For diagnosing fungal infections, scales (squamae) are taken with a glass slide or a metal blade from the border of the lesion and placed onto a glass slide. Afterward, a drop of 10 to 20% potassium hydroxide (KOH) is added. The fungal infection is confirmed if hyphae or yeast cells are detected.
For diagnosing scabies, scrapings are taken from suspected burrows or inflammatory papules using a metal blade previously dipped into the mineral oil. Scrapings are placed on a glass slide. Scabies is confirmed if mites, feces (scybala), or eggs are seen in the microscopic examination. Dermatoscopy can also help prediagnosing and guiding the site of scraping.
Diascopy is performed by pressing a glass slide on a lesion, causing the compression of small vessels. On diascopy, hemorrhagic lesions (petechiae or purpura) do not blanch; but inflammatory and vascular lesions do. Diascopy may be used in detecting granulomatous diseases such as lupus vulgaris or sarcoidosis, which turn an ”apple jelly” color on diascopy.
Köbner phenomenon denotes the development of new skin lesions of a pre-existing dermatosis within the areas of physical trauma in otherwise healthy skin. Physical trauma includes scratching, friction, rubbing, pressure, incision, laceration, insect bites, etc. Köbner phenomenon may appear 10 to 20 days (with a range from 3 days to 2 years) after the injury. It is most commonly seen in psoriasis and lichen planus.
Tzanck smear is a very simple and rapid cytologic test that is most commonly used to diagnose viral infections such as herpes simplex and herpes zoster and may help diagnose intraepidermal autoimmune blistering diseases such as pemphigus vulgaris. The blister roof is removed with a sharp blade, and the base is gently scraped with a scalpel or the edge of a spatula. At scraping the base, bleeding should not be provoked, as the inclusion of blood may disable the interpretation of results. The scraping is transferred onto a glass slide, air dry, and stained with Giemsa stain.
In herpes simplex and herpes zoster, ballooning multinucleated giant cells and eosinophilic inclusion bodies are detected, whereas in pemphigus vulgaris acantholytic cells may be seen.
Dermoscopy is a non-invasive diagnostic technique that evaluates colors and microstructures of the skin that are not visible to the naked eye, using a hand-held dermatoscope (mostly used), a stereomicroscope, or a videodermatoscope. The magnification of these instruments may be from 6x up to even 100×. Dermoscopy is mainly used for the assessment of pigmented lesions, i.e., differentiation between melanocytic and non-melanocytic lesions and then evaluation of benign and malignant features of melanocytic nevi and melanoma ( see also chapter Imaging techniques).
- K.A. Wanat, A.R. Dominguez, Z. Carter, et al.: Bedside diagnostics in dermatology - Viral, bacterial, and fungal infections (2017)
- F.T. Winsett, S.G. Patel, B.C. Kelly: Bedside Diagnostics for Infections: A Guide for Dermatologists (2020)
- R.G. Micheletti, A.R. Dominguez, K.A. Wanat: Bedside diagnostics in dermatology - Parasitic and noninfectious diseases (2017)
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