Prevalence, number and morphological types of multinucleated histiocytic giant cells in equine inflammatory dermatoses: a retrospective light microscopic study of skin-biopsy specimens from 362 horses.
Authors: Cohen R D, Scott D W, Erb H N
Journal: Equine veterinary journal
Summary
# Editorial Summary Multinucleated histiocytic giant cells (MHGC) feature prominently in equine skin biopsies, yet their diagnostic value remained unclear until Cohen, Scott and Erb systematically examined specimens from 335 horses with inflammatory dermatoses and 27 with normal skin to characterise the prevalence, quantity and morphological types of these cells. Granulomatous conditions showed significantly higher prevalence and numbers of MHGC compared to non-granulomatous dermatoses, though the predominant foreign-body type appeared consistently across most cases regardless of infectious or non-infectious aetiology. Notably, MHGC were absent from all normal skin samples, confirming their association with pathological processes, yet the number and morphological classification of these cells proved non-specific and therefore of minimal diagnostic value in differentiating between conditions. For practitioners interpreting equine skin biopsies, these findings reinforce that whilst MHGC presence indicates an inflammatory or granulomatous process, their morphology alone cannot pinpoint a specific diagnosis—making ancillary techniques such as special stains, culture and immunohistochemistry essential adjuncts to reach definitive conclusions.
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Practical Takeaways
- •While MHGC are commonly found on equine skin biopsies, their presence, number, and type cannot reliably distinguish between specific diagnoses and should not be used as primary diagnostic features
- •Special stains and tissue cultures remain necessary to confirm specific dermatological diagnoses in horses rather than relying on MHGC morphology alone
- •Finding MHGC on biopsy is consistent with granulomatous disease but occurs across many different conditions, so additional diagnostic testing is essential for accurate case classification
Key Findings
- •MHGC prevalence and number were significantly greater in granulomatous dermatoses compared to nongranulomatous dermatoses
- •Foreign-body type MHGC were the predominant morphological type in almost all cases
- •No difference in MHGC prevalence or morphological types between infectious and noninfectious dermatoses
- •MHGC were not observed in normal skin from 27 control horses, indicating association with pathological processes