Skin Examination & Biopsies - Answers

Arlo Guthrie — Mon, 20 Apr 2009 13:40:49 GMT

Current Revision posted to Revision Guide For Student Nurses - Part 2 by Arlo Guthrie on 4/20/2009 1:40:49 PM

ANSWERS

List 5 suitable methods for the collection of a skin or hair sample.
- Skin scraping.
- Hair brushing.
- Hair plucking.
- Tape strip.
- Skin biopsy (commercial biopsy punches are ideal for superficial tissues).
Describe the McKenzie brush technique.
This technique is used to identify asymptomatic dermatophyte carriers. The patient is brushed all over with a sterile brush, which is sent directly to the laboratory for inoculation into culture medium.
Describe the wet paper test.
This test is used to detect flea infestation. The patient is stood on wet blotting paper and brushed. If fleas are present - dirts will drop out of the coat, staining the paper with red spots.
What is a Wood's lamp used for?
Detection of ringworm. Some microsporum canis lesions will fluoresce a yellow-green colour. It should be noted that not all strains of ringworm fluoresce and a negative Wood's test does not rule out fungal infection.
Describe the microscopic examination of skin and hair in cases of suspected ringworm.
- Put on protective apron and gloves.
- Take hairs plucked from the edge of the lesion (including the root) together with a skin scraping and place on a labelled microscope slide.
- Add a few drops of 10% potassium hydroxide.
- Place a cover slip over the slide.
- Heat the slide over a Bunsen flame for a few seconds (this assists in clearing the hairs, so that the shaft may be seen).
- Wait for the slide to cool, then transfer it to the microscope.
- Use high dry for microscopic examination.
What reagents may enhance the detection of dermatophytes under microscopic examination?
- Lactophenol.
- Indian ink.
Why is it important to include the root of a hair follicle when taking a hair pluck sample?
Some dermatophytes such as demodex are only found deep within the hair follicles.
Describe the procedure for taking a skin scrape.
- Put on a protective apron and gloves.
- Ask an assistant to restrain the animal.
- Clip up the desired area with clippers.
- Apply 1 drop of liquid paraffin or 10% potassium hydroxide to the site for sampling.
- Fold the skin to bring bacteria and parasites nearer to the surface
- Use a scalpel blade to scrape the area until petechial blood is observed (pin-point clusters of surface capillary blood).
- Scrape the sample onto a labelled slide for immediate microscopic examination.
- Alternatively, the blade and sample may be placed together in a suitable receptacle for dispatch to an external laboratory.
- In addition swabs may be taken from the site; smears may be made or the sample sent in charcoal transport medium to the external laboratory.
Why is liquid paraffin or 10% potassium hydroxide placed on the skin prior to a scraping?
- Liquid paraffin = helps separate debris from the parasites, also parasites may move in the liquid - thus being more detectable.
- 10% Potassium hydroxide = helps to break down the skin and hair thus allowing parasites to be visualised more easily, also "clears" the parasite making its features more identifiable.
What is the fixative of choice for most routine histopathology?
10% Formol saline.

NB. This subject is covered in more detail in Chapter 4 - Parasitology & Bacteriology. Skin biopsies are covered in Chapter 8 - Surgical Nursing & Theatre Practice.