Bedside Clinical Tests in Dermatology
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Direct answer
Bedside clinical tests in dermatology are simple manoeuvres, done with a glass slide, a fingertip, a blunt instrument or a hair tuft, that reveal diagnostic features without a laboratory. Diascopy shows whether a colour is vascular or granulomatous, and the dimple test identifies a dermatofibroma. Sensory testing with light touch, pinprick and temperature maps the anaesthesia of leprosy and other neuropathies.
What you must remember
- Diascopy: pressing a glass slide on a lesion; vascular erythema blanches, whereas granulomatous colour persists.
- Apple-jelly nodules: brownish-yellow colour on diascopy, typical of lupus vulgaris and sarcoidosis.
- Grattage test: scraping the scale of a lesion to elicit the Auspitz sign, characteristic of psoriasis.
- Dimple test: squeezing the skin beside a dermatofibroma produces inward dimpling, because the lesion is anchored in the dermis.
- Dermographism: firm stroking produces a linear wheal, and symptomatic dermographism is linked to urticaria.
- Hair pull test: gentle traction on a tuft of hair; more than about 10 per cent of the tuft (over six hairs) coming away indicates active shedding.
- Sensory testing: light touch, pinprick and temperature are tested separately over hypopigmented patches, and loss suggests leprosy.
- Darier sign: a wheal on stroking a lesion of urticaria pigmentosa, from mast cell degranulation.
A bedside sequence for a skin examination
Bedside tests are quick and cost nothing, so they belong early in the examination and before a biopsy is planned. Each test narrows the differential, and the findings are recorded in the case note in the same order they were obtained.
- Press with a glass slide: perform diascopy on any red or brown lesion, and note whether the colour blanches or persists.
- Scrape any scale: use a glass slide or blunt edge to perform the grattage test on scaly plaques and look for pinpoint bleeding.
- Squeeze a firm nodule: test for the dimple sign by pinching the skin beside a suspected dermatofibroma.
- Pull a tuft of hair: apply gentle traction to a small bunch of hairs, then count the loose hairs and their roots.
- Map sensation: test light touch, pinprick and temperature over any hypopigmented or anaesthetic patch, and compare with normal skin.
The findings guide the next investigation, but they do not replace a biopsy or a laboratory test when the diagnosis is unclear. Record each test result in the case note, including negative findings, since a negative test also narrows the differential.
Where bedside tests catch candidates
Bedside tests are easy to recall, but examiners set traps around what each finding means.
- Trap: calling persistent apple-jelly nodules simple erythema Correct: vascular erythema blanches on diascopy, whereas apple-jelly nodules persist, showing a granulomatous colour.
- Trap: treating a positive hair pull test as diagnostic of alopecia areata Correct: a positive result shows active shedding, which occurs in telogen effluvium and alopecia areata alike, so it does not identify the cause.
- Trap: testing only pinprick in a leprosy patch Correct: test light touch, pinprick and temperature separately, since different sensory modalities can be affected unequally.
- 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 keratinisation disorder.
Frequently asked questions
What does diascopy show in lupus vulgaris?
Diascopy in lupus vulgaris shows apple-jelly nodules, which are brownish-yellow and persist under the glass slide. This colour reflects granulomatous tissue, whereas vascular erythema would blanch under the same pressure.
What does a positive dimple sign indicate?
A positive dimple sign, in which squeezing the skin produces inward dimpling, indicates a dermatofibroma. The dimpling occurs because the lesion is anchored to the overlying dermis, and it helps separate the lesion from cysts and lipomas.
What does a positive hair pull test suggest?
A positive hair pull test shows active hair shedding, with a clearly increased number of loose telogen hairs. Telogen effluvium and alopecia areata can both produce it, so the test must be interpreted with the history and trichoscopy.
Which bedside sensory test helps identify leprosy?
Sensory testing with light touch, pinprick and temperature over a hypopigmented patch helps identify leprosy, because loss of sensation in the patch suggests nerve involvement. Each modality should be tested separately, since they can be affected unequally.
What does dermographism indicate in urticaria?
Dermographism is a linear wheal that appears after firm stroking of the skin, and symptomatic dermographism is linked to urticaria. It is a clinical finding that helps classify urticaria and guides the investigation of its triggers.