Impression Smear Agreement with Acetate Tape Preparation for Cytologic Sampling

Comparison of cytological findings between direct impression smears and adhesive slides in canine superficial bacterial folliculitis

BACKGROUND

Cutaneous cytological investigation is a valuable tool for the diagnosis of superficial bacterial folliculitis (SBF). Studies comparing tape strips and direct impression (DI) smears have demonstrated that DI may recover more inflammatory cells and nuclear streaming (NS). Adhesive slides (AS) have not been evaluated in cutaneous cytological investigation.

OBJECTIVE

To compare cytological findings between AS and DI for the same lesion in SBF.

ANIMALS

Fifteen client-owned dogs with clinical signs suggestive of SBF were enrolled.

MATERIALS AND METHODS

Fifty lesions consistent with SBF comprising collarettes, papules and crusts were included. Half of each lesion was sampled using DI and the other half sampled using AS. Papules were sampled sequentially in a randomised order between techniques. Three investigators blinded to the sample pairings read the slides in duplicate. Ten adjacent oil immersion fields were examined. Bacteria were recorded on a quantitative scale, polymorphonuclear cells (PMN), NS and 'miscellaneous' on a qualitative scale, and keratinocytes (KC) on a semiquantitative scale.

RESULTS

Significant differences were identified for KC (DI mean 2.5, SD ±0.08; AS mean 3.3, SD ±0.06, p < 0.0001), 'miscellaneous' (DI mean 0.72, SD ±0.03; AS mean 0.83, SD ±0.02 p < 0.0001), NS (DI mean 0.69, SD ±0.03; AS mean 0.56; SD ±0.03, p < 0.0001) and extracellular cocci (DI mean 5.03, ±SD 7.2; AS mean 3.91, ±SD 4.3, p = 0.01).

CONCLUSIONS AND CLINICAL RELEVANCE

DI identified more EC cocci and NS, while AS detected more KC and debris. Intra- and interobserver agreement varied, with AS having poorer agreement for several parameters. These results can be used to inform the clinician of the best methodology to use in confirming a diagnosis of SBF.

A novel cytological technique for bacterial detection on canine skin

BACKGROUND

Cytological examination of the skin is an important diagnostic technique in dermatology for disease diagnosis and monitoring of treatment. Impression smear and tape-strip preparation are gold standard cytological techniques. This study introduces a novel cytological method, slurry preparation, in which debris collected from the skin surface is macerated in warm sterile water and dried on the slide.

HYPOTHESIS/OBJECTIVES

To compare organism yield between a novel and two standard cytological collection techniques by evaluating bacteria and Malassezia yeast counts.

ANIMALS

Thirty client-owned dogs diagnosed with atopic dermatitis and lesions consistent with pyoderma and/or Malassezia dermatitis.

MATERIALS AND METHODS

In a prospective, blinded comparison study, dermatological lesions from each dog were sampled using impression smear, tape-strip and slurry preparation methodologies. Ten random reticle fields per lesion, accounting for a total area of 6.25 × 10^-3  mm² (equivalent to ˜5% of a typical ×40 field field), were evaluated by light microscopy for each cytological method. Bacterial and Malassezia organisms were measured as counts/sample. The slurry preparation was compared to each of the standard methodologies separately using paired Student's t-tests.

RESULTS

The slurry preparation was demonstrated to be more sensitive than gold standard techniques in detecting bacteria, with mean differences of 12.7 and 13.5 additional bacteria per cytological sample, compared to the impression and tape-strip preparations, respectively. The slurry preparation did not differ significantly in detecting Malassezia organisms compared with impression smear preparation. The tape-strip preparation was demonstrated to be more sensitive than the slurry preparation in the detection of Malassezia organisms, finding a mean difference of 0.22 more organisms per sample.

CONCLUSION

Slurry preparation presents advantages over the gold standard techniques in the detection of bacteria which can help to manage canine pyoderma more appropriately. Performing a slurry preparation in cases of suspected canine pyoderma could be considered as an alternative to the gold standard techniques.