A case of Borrelia-associated cutaneous pseudolymphoma in a horse.

The research article describes a case study of a horse developing dermal papules, a skin condition caused by Borrelia bacteria transmitted through a tick bite, which mimicked lymphoma symptoms. After careful observation, serological testing, and implementing doxycycline treatment, the diagnosis of Borrelia-associated cutaneous pseudolymphoma was confirmed.

Case Report Description

• The case report focuses on a 10-year-old horse who developed multiple dermal papules, small raised bumps on the skin, over the right masseter area. The development of these papules followed the removal of a tick from the same site around 3 months earlier.

Histological Examination and Diagnosis

• An examination of a papule biopsy revealed it resembles two distinct conditions: a T-cell-rich B-cell lymphoma, a rare subset of lymphoma where abnormal T-cells rich in B-cells cause skin lesions, or cutaneous lymphoid hyperplasia, a benign skin condition that mimics lymphoma.
• The latter condition, also known as pseudolymphoma, can sometimes be associated with a tick bite. Since the horse had a tick removed from the papule site, this connection was considered in the diagnosis.

Contributing Tests and Final Diagnosis

• Further investigation to pinpoint the disease included a serological test and PCR of the biopsy sample for Borrelia, the bacteria often carried by ticks that can cause Lyme disease.
• Immunohistochemical testing, a method to detect specific antigens in tissues, was performed on the skin biopsy to supplement the previous results. Additionally, the horse’s clinical background and response to doxycycline treatment, an antibiotic often used to treat bacterial infections, were taken into account during the examination process.
• All these findings strongly supported the diagnosis of Borrelia-associated cutaneous pseudolymphoma. This is a skin condition caused by Borrelia bacteria which imitates lymphoma but is less severe. Therefore, the horse didn’t have the aforementioned T-cell-rich B-cell lymphoma, but pseudolymphoma triggered by Borrelia bacteria from the tick bite.

Implications and Further Research

• This case study provides valuable insights into the diagnosis of dermatological conditions in animals, particularly those related to tick-borne diseases. It emphasizes the complexity of diagnosing such conditions and the importance of considering all possible factors.
• Further research may delve into the frequency of such cases, precautionary measures against tick bites in horses, and the potential impact of early and accurate diagnosis on the treatment outcome.