Comparison of timing of relapse in dogs with nonassociative immune-mediated hemolytic anemia, thrombocytopenia, or polyarthritis

Background: Relapse is a clinical concern in dogs diagnosed with immune-mediated hemolytic anemia (IMHA), thrombocytopenia (ITP), or polyarthritis (IMPA). The average time to relapse is unknown, and evidence that vaccination is associated with disease relapse is lacking.

Hypothesis/objectives: Compare the incidence of relapse in groups of dogs with IMHA, ITP, or IMPA over a 24-month period after diagnosis and compare proportions of dogs that received vaccines in those dogs that did and did not relapse.

Animals: One hundred sixty client-owned dogs (73 with IMHA, 55 with ITP, 32 with IMPA).

Methods: Medical records of dogs were reviewed with the goal of following cases for a minimum of 2 years. Incidence of relapse was calculated for each disease, and relapse rates in dogs that were or were not vaccinated after diagnosis were compared.

Results: Relapse rates at 12 months differed significantly among disease groups (P = .02), with a higher rate for IMPA (35%) compared to IMHA (11%) or ITP (11%). Relapse rate at 24 months was 41% for IMPA, 18% for IMHA, and 23% for ITP. Ninety percent of IMPA relapses occurred in the first 12 months after diagnosis, compared with 56% for IMHA and 50% for ITP. Vaccine administration after diagnosis was not associated with relapse (P = .78).

Conclusions and clinical importance: Risk of disease relapse in IMPA is highest in the first year after diagnosis, with a higher relapse rate compared with IMHA and ITP. The role of vaccination in disease relapse remains unclear.