Fiona Whitworth 1, Sophie Adamantos 1, Polly Frowde 1, Richard Whitelock 1, Vicki L Black 1

Background:
Immune-mediated polyarthritis (IMPA) is a common inflammatory joint disorder in dogs, categorized into erosive and nonerosive forms. Ligament laxity has been reported in erosive IMPA due to joint instability but not previously described in nonerosive IMPA. This study aimed to characterize carpal and tarsal ligament laxity in dogs with nonerosive IMPA and to assess clinical outcomes, including the potential need for surgical intervention.

Methods:
A retrospective case series was conducted by reviewing records from two veterinary referral centers between 2009 and 2017. Inclusion criteria were a diagnosis of nonerosive IMPA with concurrent carpal or tarsal ligament laxity, excluding cases influenced by corticosteroid use or with laxity in stifle/hip joints. Data collected included signalment, clinical presentation, diagnostics, treatments, and follow-up outcomes. Diagnosis of IMPA was based on synovial fluid cytology and imaging ruling out erosive disease.

Results:
Five dogs were identified, with ligament laxity affecting either carpi and tarsi (n=3) or carpi only (n=2). One dog had type III IMPA; the others had type I. Ligament laxity developed after prednisolone discontinuation in some cases and was unrelated to hyperadrenocorticism. Three dogs underwent surgical arthrodesis due to persistent lameness. All dogs required lifelong immunosuppressive therapy, and three were euthanized due to severe clinical signs and poor disease control. In the two surgically managed cases with follow-up beyond one year, improvement was noted, although one required revision surgery due to complications.

Limitations:
The study was retrospective and included a small sample size. Not all potential underlying causes of ligament laxity could be thoroughly excluded. Diagnosis of ligament laxity was based on physical exam findings, without consistent use of stress radiographs or advanced imaging.

Conclusions:
Ligament laxity can occur in nonerosive IMPA and may indicate a severe disease variant resembling erosive IMPA. This manifestation is associated with poor prognosis and necessitates long-term immunosuppression and, in some cases, surgical intervention. Early aggressive treatment may be beneficial, but further studies are needed to clarify pathogenesis and optimal management.

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