Successful treatment and long-term follow up of idiopathic immune-mediated polyarthritis with mycophenolate mofetil in a cat

Abstract

Case summary A 7-year-old neutered male Norwegian Forest Cat was presented with decreased appetite and activity, weight loss, fever, neutrophilia and hyperglobulinaemia. A physical examination showed painful stifle joints and enlarged popliteal lymph nodes. Blood examination showed neutrophilia, hyperglobulinaemia and increased serum amyloid A. Urinalysis, thoracic and abdominal radiographs, and abdominal ultrasonography were unremarkable. Synovial fluid from the knee joints had diminished viscosity and revealed neutrophilic inflammation on the smear. There was no evidence of infection in a microbiological culture of the synovial fluid. A diagnosis of idiopathic immune-mediated polyarthritis (IMPA) was made. Prednisolone was initiated at 2 mg/kg q24h PO and tapered with additional immunosuppressants (leflunomide, ciclosporin A and methotrexate); however, prednisolone could not be discontinued. Informed consent was obtained from the owner and mycophenolate mofetil (MMF) at a dosage of 10 mg/kg q12h PO was initiated on day 798. There were no adverse effects of MMF and prednisolone was discontinued on day 1183. Clinical signs resolved and the cat’s general condition remained stable with MMF alone at a dosage of 10 mg/kg q48h PO on day 1600. Relevance and novel information There is limited information describing feline IMPA and its treatment options other than the use of prednisolone. This is the first report of the successful treatment and long-term follow-up of feline IMPA with MMF. MMF may be a safe and effective option as an additional immunosuppressant in feline IMPA.

Canine immune‐mediated polyarthritis: A review of 84 cases in the UK between 2011 and 2021

“…The number of dogs with long‐lasting remission, representing 62% of dogs in the present study, differed from 0% to 63% in previous publications (Bennett, 1987 ; Clements et al., 2004 ; Ravicini et al., 2022 ). It could be speculated that this discrepancy results from disparities in treatment used between studies, (Stone, 2017a ; Bennett, 1987 ; Clements et al., 2004 ; Shaughnessy et al., 2016 ; Johnson & Mackin, 2012b ; Colopy et al., 2010 ; Sato et al., 2017 ; Tamura et al., 2020 ; Whitworth et al., 2019 ; Bergh et al., 2021 ) particularly as some of the therapies used have fallen into disuse due to their adverse effects (Wallisch & Trepanier, 2015 ; Matsuyama et al., 2017 ) or lack of evidence of effectiveness (Bergh et al., 2021 ). However, prednisolone was administered in both the study with zero long‐lasting remissions and a more recent study with a 63% rate of ‘complete cure’ (Bennett, 1987 ; Ravicini et al., 2022 ).…”

“…Eighty-two per cent (33/40) of the dogs of our cohort with long-lasting remissions had been treated with prednisolone. Of these, 48% (16/33) had been treated with prednisolone and other immunosuppressive drugs believed to achieve clinical remission, (Stone, 2017a;Keyte et al, 2021;De Laet, 2022;Colopy et al, 2010;Sato et al, 2017;Tamura et al, 2020;Rhoades et al, 2016) similarly to the study with a 63% rate of complete cure (Ravicini et al, 2022). This could suggest that the use of a secondary immunosuppressive drug may not achieve higher long-term remission rates.…”