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Dermatology Investigations

  1. Skin Biopsy
    1. Histopathology
    2. Direct Immunofluorescence study
    3. Culture
    4. Smear for AFB, fungus.
Punch biopsy: 3 to 4 mm tissue punch, specimen not to be crushed with tooth forceps, skin hook may be good in handling the tissue.

Scalpel biopsy: elliptical excisional, incisional or shave biopsy. 3/0 non-absorbable sutures for legs, 5/0 for face and 4/0 else-where.
  1. Wood's Lamp Examination
    Ultraviolet light of 365 nm wavelength is obtained by passing the beam through a Wood's filter composed of nickel oxide containing glass. The examination has to be done in a dark room.

    Infected hair in tinea capitis caused by Microsporum canis will fluoresce bright green, skin lesion of active pityriasis versicolor will fluoresce golden yellow, fresh urine in porphyria cutanea tarda fluoresces a reddish colour, erythrasma will fluoresce coral red, vitiligo lesion appears more white and ashleaf macule in Tuberous sclerosis is more apparent, coral red fluorescence of teeth in congenital erythropoietic porphyria.
  2. Patch Test
    This tests the type IV hypersensitivity reaction and it is a confirmatory test for allergic contact dermatitis.

    Trolab standard patch test is used to screen and confirm allergic contact dermatitis. Further breakdown of the test may require patch test with different series e.g. fragrance series. The test materials are applied to the back under aluminium discs with occlusion. The sites are inspected at 48 hours and test materials removed. The sites are re-inspected at 96 hours for delayed reaction. The grading of the reaction will be as follows:

No reaction: 




Weak (erythema, non-vesicular):


Strong (vesicular or edematous):


Extreme (with ulceration):


Irritant reaction:


Not tested:


  1. Mycology Examination
    Superficial fungi can be identified by examination of the skin scraping, nail or hair. The scales, nail or hair should be collected onto a slide and a drop of 10 to 20 percent KOH to dissolve the keratin.

    This technique can be utilized to identify hyphae in dermatophyte infections, pseudohyphae and budding yeast in candida infections, and fragmented hyphae and spores in tinea versicolor.
  2. Mite Examination
    To identify the burrow in common area e.g. finger webs. With the help of magnifying glass, the acarus may be seen as a tiny grey dot at the end of burrow. It can be removed by a sterile needle. If mites not seen, burrow will be moistened with liquid paraffin or mineral oil and scraping with the scalpel blade and transferred to slide for examination.
  3. Blood & Urine Tests muscle enzymes to exclude dermatomyositis, urine sugar test to exclude diabetes mellitus.
  4. Radiology Examination
    The commonest tests done are X-ray chest to exclude pulmonary tuberculosis and X-ray joints for psoriatic arthropathy. CT scan is important for exclusion of internal enlarged lymph nodes in cutaneous lymphoma and to exclude brain lesions in a case of neurofibromatosis.
  5. Other Tests
    1. Prick testing is much less helpful in dermatology.. Multiple positive skin tests to commercially prepared diluted antigens may only imply the atopic tendency of the tested subject.
    2. Dark-ground examination for suspected genital ulcer to look for Treponema Pallidum can be easily done when equipped with a dark-ground microscope. It is the interpretation of the wet smear which may require some experience.
    3. (Acetowhitening) Acetic acid test on genital or cervical papules facilitates detection of subclinical condylomata acuminata. Gauze saturated with 5% acetic acid is wrapped around area for 5 to 10 minutes and the use of colposcope or magnifying hand lens to detect the lesional white papules.
    4. Tzanck smear is a cytologic technique used for diagnosis of viral infection like herpes simplex or varicella-zoster and also for auto immune vesiculobullous disorder like pemphigus vulgaris. An early vesicle, not a pustule or crusted lesion, is unroofed, and the base of the lesion is scraped gently with a scalpel blade. The material is placed on a glass slide, air-dried, and stained with Giemsa or Wright’s stain. Multinucleated epithelial giant cells in viral infection and acantholytic cells in pemphigus vulgaris can be demonstrated by this method.
  6. Clinical Photography
    Clinical photo is the best to document any lesion.

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