Alopecia areata with lymphocytic mural folliculitis affecting the isthmus in a thoroughbred mare.

The research article describes a case of a 13-year-old horse with a rare form of alopecia areata, evident due to the lymphocytic infiltration at the different levels in the horse’s hair follicles.

Introduction and Case Description

• The patient in the study is a 13-year-old thoroughbred mare, who had been exhibiting signs of generalized, noninflammatory alopecia for 8 years.
• This mare also had a recent 3-month history of alopecia, erythema, and scaling on the white star area of the face (namely forehead and muzzle).

Biopsy and Histopathological Examination

• Biopsy samples were collected from multiple sites including the mane, neck, shoulder, flank, and gluteal region for detailed examination.
• The histopathological investigation confirmed a lymphocytic inflammatory infiltrate, which was subtly affecting and surrounding the anagen, or active phase, hair bulbs. These findings were consistent with a diagnosis of alopecia areata.
• Particularly, the biopsy sample from the white star on the horse’s forehead showed the presence of atrophic hair follicles – a sign of damage or degeneration. Furthermore, it also showed perifollicular and mural mononuclear folliculitis affecting the isthmus – the area around the sebaceous gland entrance of the hair follicle.

Immunohistochemical Staining

• The researchers also conducted immunohistochemical staining using a CD3 marker, which helped them confirm the T-lymphocytic origin of the inflammatory infiltrate in all the samples.

Concluding Remarks

• Usually, lymphocytic infiltration occurs at one level of the hair follicles, but the occurrence at both bulbar and isthmic levels of the hair follicles in this horse was noted as unusual.
• Therefore, the researchers propose that this finding could be a variant in the histological presentation of alopecia areata – a postulation that may contribute to research and understanding of this condition.