FIGURE 1 Adult Demodex canis mite seen on a trichogram
A trichogram is the evaluation of hairs using a microscope and can be a valuable diagnostic tool in any dermatology case. A trichogram can help the practitioner examine hairs for parasites (eg, Demodex spp [Figure 1]) that may be adjacent to the root of the hair or attached to the hair itself (eg, louse nits [Mallophaga, Anoplura]); changes in the cortex of the hair, as can occur with dermatophytosis; fractures in the hair tips due to alopecia; pigmentary changes; and other conditions and/or abnormalities.1 The hair roots can also be examined to determine if the hairs are in anagen (ie, round, smooth, often pigmented bulbs) or telogen (ie, club- or spear-shaped bulbs) and if the patient is barbering its coat, as barbered hairs appear shorter and split or fractured due to trauma.1,2
If viable, hairs should be plucked from active lesions (eg, lesions of alopecia, crusting, scaling, or follicular casting), and plucking vibrissae (ie, whiskers) should be avoided. If patchy alopecia is present, collecting hairs from the margin of an alopecic lesion is best. However, central hair regrowth may be present on the lesion in areas of healing, in which case collecting from this area may not aid in diagnosis. Collecting hairs from the leading edge of the lesion (similar to collecting samples for cytologic evaluation) may allow for a better representation of the active process of the lesion. In cases of suspected demodicosis, approximately 30 to 40 hairs per affected body location should be collected and evaluated; however, collecting at least 30 to 40 hairs in all canine or feline cases can help ensure a representative sample.
In cases of suspected demodicosis, the author prefers to perform deep skin scrapings over most of the body rather than to perform a trichogram; however, in the author’s experience, trichograms are preferably conducted in all cases around the eyes, where scalpel blades in a nonsedated patient can be dangerous, or over bony prominences, where there is not a flat area that allows for skin scraping. The nail beds are a good location in which to perform a trichogram because the digits are common areas for demodectic mange in dogs or dermatophytosis in cats1,3 yet are difficult areas in which to perform skin scrapings. When performing a trichogram on the nail beds, plucking hairs from multiple toes can ensure that representative samples from any affected areas are obtained.