Cytology and Cultures
The first diagnostic step for any dermatology patient is cytology - looking at slides under the microscope.
What is cytology? Why is it important?
The first diagnostic step for any dermatology patient is cytology - looking at slides under the microscope. Examples of cytology include: ear swabs, ear mite prep, Cheyletiella prep, direct impression, tape impression, trichogram (hair pluck), deep skin scrape, superficial skin scrape. Along with other non-invasive diagnostics (ex. Wood's lamp, flea comb, diascopy, etc.), these quick and relatively inexpensive tools can immediately reorganize the list of possible diseases. The simplicity of dermatology is that the problem is easily visible, but the challenge is that many things looks similar.
A culture, obtained by swabbing the skin, helps further identify which organism and the ideal antimicrobial based on susceptibility testing in the laboratory.
In particular, it is imperative to rule out infection. If infection is present, then cytology can often narrow the list of antimicrobials used for treatment. A culture, obtained by swabbing the skin, helps further identify which organism and the ideal antimicrobial based on susceptibility testing in the laboratory. Pairing cytology with a culture is important because there any many normal bacteria and yeast on the skin and in the ear (https://pubmed.ncbi.nlm.nih.gov/31960536/); a culture must be interpreted with cytology to find the pathogenic organism.
It must be recognized that many infections are secondary. Even while addressing the infection, workup of the primary underlying cause should be started. Otherwise, the infection may not resolve and/or another infection will develop. The single biggest risk factor for antibiotic resistance is exposure to an antibiotic. Methicillin-resistant Staphylococcus pseudintermedius/schleiferi (MRSP/MRSS, similar to MRSA in humans) and other multi-drug resistant bacteria are constant concerns. For superficial skin infections, we'll often discuss topical therapy as a first-line treatment, particularly for maintenance.