Immune-Mediated Polyarthritis (IMPA)
in the Cavalier King Charles Spaniel

Immune-mediated polyarthritis (IMPA) is an idiopathic form of arthritis, causing recurring episodes of lameness and joint swelling, usually in mulitple joints. It is a commonly diagnosed inflammatory disease in dogs and  has been reported in cavalier King Charles spaniels in at least five published veterinary journal articles.

What It Is

IMPA can be “erosive” or “non-erosive. The erosive condition is known as rheumatoid arthritis (RA). The non-erosive type is called idiopathic because there is no evidence of any primary disease nor any serological Synovial joint(blood serum) evidence regarding its immunological properties.

Idiopathic forms of polyarthritis in dogs have been classified into four types:

Type I: Uncomplicated Arthritis: polyarthritis with none of the associations reported in the other types.
Type II: Reactive Arthritis: Polyarthritis associated with an infective disease process remote from the joints, such as a respiratory or urinayr tract infection.
Tpye III: Enteropathic Arthritis: polyarthritis associated with gastro-intestinal disease; such as gastro-enteritis, ulcerative colitis
Type IV: Neoplastic Related Polyarthritis: polyarthritis associated with neoplastic disease remote from the joints.


Polyarthritis produces swelling and tenderness at one or more of the affected dog's joints. The main symptoms are joint pain, stiffness, lameness. The affected dog also likely will have a high fever and appear anorexic and/or lethargic. In some cases, the dog has no swelling or lameness but shows signs of a vague systemic illness.

The most commonly affected joints are the carpal (wrist), tarsal (hock), stifle (knee joint), and elbow.

Non-erosive IMPA typically also produces lesions (open sores) on the skin near the affected joints.

Erosive IMPA lesions can result in damage to the soft-tissues which support the affected joints, and also the Left carpus of CKCSbones at those joints. Dogs with erosive IMPA may develop unstable joints due to damage or destruction of the soft-tissue structures.

In a November 2016 article, a team of Wisconsin and Michigan researchers studied the clinical records of 79 dogs diagnosed with immune-mediated polyarthritis (IMPA). Of those 79 dogs, 13 had erosive IMPA, of which, two were cavalier King Charles spaniels. The 13 affected dogs had erosive lesions in their carpal joints. The estimated median synovial fluid lymphocyte count for dogs with erosive IMPA was significantly greater than that for dogs with nonerosive IMPA. Results indicated erosive IMPA most commonly affected the carpal joints of middle-aged small-breed dogs. (See from this article, at above left, the carpus of an 8-year-old spayed female Cavalier King Charles Spaniel with subjectively moderate subchondral bone lysis accompanied by severe synovial swelling -- in x-ray at right.)

Cavalier Skeleton - Dog ChannelCourtesy of The Dog Channel


Several procedures normally are performed to diagnose IMPA, the primary one being the collection and examination of fluid samples from the sac of the synovial membrane situated at the affected joints. Biopsies of the synovial membrane, muscle, and skin also may be taken.

X-rays (radiographs) of the affected joints, chest, and abdomen will be taken, especially to determine if any bone damage or loss has occurred. X-rays are used to look for changes in the joints which would indicate that the IMPA is erosive rather than non-erosive.

Blood serum and other testing should be performed to determine the presence of, or rule out, other causes such as bacterial infections. Urinalysis may be performed, to screen for the presence of proteinuria, a common abnormality found in dogs otherwise diagnosed with non-erosive IMPA, according to this May 2022 article.



Treatment may vary depending upon the type of IMPA. If evidence of infections have been identified, antibiotics will be administered. Typically, drugs to suppress the immune system,  such as leflunomide or prednisone, are the drugs of choice to deal with inflammation at the joints, with dosages increased if necessary.

Cytotoxic drugs, which affect the growth and action of some cells that cause joint pain,  swelling,  and damage due to arthritis, likely will be prescribed, particularly if the IMPA is resistant to prednisone. They include cyclophosphamide (Cytoxan), azathioprine (Imuran), and methotrexate (Rheumatrex, MTX, Amethopterin). Cytotoxic drugs rarely are used for more than 8 weeks and require periodic monitoring of blood cell counts.

Bedinvetmab (Librela) is a injectable solution to alleviate pain associated with osteoarthritis (OA) in dogs. It is administered monthly. It is a monoclonal antibody which binds to and targets Nerve Growth Factors (NGF), which have key involvement in OA pain. It is manufactured by Zoetis. In May 2023, Zoetis announced that the USA Food & Drug Administration approved Librela (bedinvetmab injection) for the control of pain associated with osteoarthritis (OA) in dogs. Zoetis stated in its press release that Librela is the first and only once-monthly, anti-NGF monoclonal antibody treatment for canine OA pain and is approved as safe and effective in providing long-term control of OA pain symptoms in dogs, which can improve their mobility and overall quality of life.

Nevertheless, bedinvetmab is the subject of controversy due to reports of unanticipated adverse reactions, including ataxia, hind-end weakness, inability to walk, new or worsened seizures, and organ damage. Among expressed concerns are that blocking NGF may prevent its known protective and reparative roles elsewhere in the body. See this May 2015 article and this October 2023 article.

Synovetin OA is a "conversion electron therapeutic veterinary device" which is injected into the dog's elbow joints which are afflicted with osteoarthritis to reduce pain and inflammation of the synovial membrane which lines the elbow (synovitis).

Palmitoylethanolamide (PEA) is a N-acylethanolamine molecule in a family of long-chain fatty acid Micronized PEAamides called ALIAmides. PEA has been found in rat and mice studies to limit hyperactvity in immune cells and thereby control inflammatory responses and resulting tissue damage. PEA is produced by the animal's body as needed in response to certain types of injuries. PEA is a product of normal fatty acid synthesis from palmitic acid. It is found in many common foods, particularly palm oil, soy beans, egg yolks, and peanuts.  The commercial version is most commonly manufactured from palm oil*. No objective, unbiased clinical studies of the effect of PEA on treating arthritis has been published.

Not all PEA is alike. There are three types of PEA.

• Basic PEA, called "naive PEA", is insoluble in water and therefore the oral intake of it (rather than being injected directly into the abdomen) has very poor bioavailability, meaning that it does not get absorbed well in the dog's gut.

Micronized PEA (m-PEA) is a patented technique that reduces the diameter of PEA particles, making them absorbable in the intestine, which has been found to be more effective than ordinary naive PEA in activating PEA levels in blood plasma in dogs.  See this August 2014 article.

• Ultra-micronized PEA
(um-PEA), also patented, reduces the PEA particle size further, to enable it to cross the blood-brain barrier, likewise has been found to be much more effective than naive PEA.  See this August 2014 article.

If a PEA product is not advertised as being micronized or ultra-micronized, then Dr. Clare Rusbridge advises that "You probably are wasting your money." A variety of brands of micronized and ultra-micronized PEA are offered on-line.

As for dosages, in a study using micronized PEA, the range was up to 24 mg/kg for osteoarthritis.

* Palm oil: The palm oil cultivation industry has been destroying rainforests in Sumatra and Borneo in Indonesia and Malaysia, the only habitats of orangutans. If you are going to obtain PEA, we suggest that you do so only from vendors whose PEA has been manufactured with palm oil from sustainable sources and not the deforestation of rainforests. This link connects to a "PalmOil Scan Mobile App" which will enable you to determine if the PEA vendors you select obtain their palm oil from sustainable sources.

Nutraceuticals are nutrients necessary for supporting or improving normal structure and function of the weight-bearing joints. They have been found to:

• Support or enhance metabolism of cartilage cells (chondrocyte) and joint membranes (synoviocyte) -- an anabolic effect;

• IVetriScience GlycoFlex Joint Supportnhibit damaging enzymes within synovial fluid and cartilage -- a catabolic effect;

• Inhibit formation of thrombi in small blood vessels supplying the joint (antithrombolic).

The most common nutraceuticals are glucosamine and chondroitin. Glucosamine regulates the synthesis of collagen in cartilage, and may provide mild anit-inflammatory effects. Crystalline glucosamine sulphate has the greatest efficacy and bioavailablity for osteoarthritis. Chondroitin sulfate inhibits destructive enzymes in joint fluid and cartilage. Both of them also contribute to the building blocks synthesis of glycoaminoglycans and proteoglycans) for the formation and repair of cartilage.

Undenatured type-II collagen (UC-II), a patented form of collagen extracted from the cartilage of the chicken’s sternum, has been found effective in reducing pain and discomfort experienced by dogs suffering from (osteoarthritis.

Microlactin (Duralactin) is a nutraceutical consisting of a protein concentrate derived from the milk of hyper-immunized cows, called hyper-immune milk factor (HIMF). It reportedly impedes inflammation and can be used safely in dogs. It is slow to respond to pain, taking a week to two weeks for maximum effectiveness.

Cannabis leafCannabinol (CBD oil) is produced from hemp and marijuana (Cannabis Sativa) plants. CBD oil mimics the endocannabinoid molecules which the dog’s (and our) body produces in several different organs. They play roles in reducing pain, regulating inflammation, and affecting the immune system, by initially binding to receptors in the brain. Recommended dosages very widely, from 0.25 mg per kg per day to as much as 9 mg/kg/day (for epilepsy). However, the maximum recommended dose for adult humans is only 0.15 mg/kg/daily, the equivalent of 5 drops of 5% CBD oil.

Varieties of CBD: Cannabidiol-based veterinary products are derived mainly from hemp (Cannabis sativa) and must contain less than 0.3% tetrahydrocannabinol (THC). This form of CBD can be processed into “full spectrum” or “broad spectrum” and also may be in the form of a “distillate”, in which all THC has been removed, or in the form of CBD “isolate”, which is a purifed powder.

Full Spectrum: Full spectrum CBD contains other extracts found in the cannabis plant, including terpenes, and up to 0.3% THC.

Broad Spectrum: Broad spectrum CBD also contains some other cannabis compounds but no more than trace amounts of THC.

CBD Isolate: CBD isolate is pure CBD and contains no other cannabis plant compounds.

In a November 2023 article, researchers report finding that regular (chronic) administration (daily for 36 weeks) of 5 mg/kg of CBD (broad spectrum extract) was better tolerated by healthy dogs than 10 mg/kg. The main evidence was softer feces at the higher dosage. Also, they found that both dosages caused an increase in alkaline phosphatase (ALP) activity. Several previous studies also have found high ALP levels in CBD-treated dogs. ALP is an enzyme that’s found throughout the dog's body, but especially in the liver, intestines, and bones. ALP blood tests measure the level of ALP in the blood that comes from the liver and bones. High levels of ALP in the blood may indicate liver disease or certain bone disorders. Therefore, liver testing should be performed periodically if CBD oil is administered long term.

Tetrahydrocannabinol (THC), the psychoactive compound in marijuana, is highly toxic to dogs, and in some cases it can be severe. Dogs have more cannabinoid receptors in their brains, making the effects of THC much more toxic than in humans.  THC intoxication has become a common presentation in all types of veterinary practices in the United States of America. Signs of THC intoxication include bradycardia, ataxia, hyperesthesia, respiratory depression, nausea, mydriasis, urinary incontinence, hypothermia, and seizure.

Laser therapy, called "photobiomodulation" (PBM), which is continuous wave laser treatments at acupuncture sites, is a treatment option, either with or without medication.


What You Can Do

Ergo FeederOwners may provide their affected dogs with supplements such as glucoamine HCI, methylsulfonylmethane (MSM), N,N-Dimethylglycine HCI (DMG), and manganese. Retail combinations of these supplements include Vetri-Science GlycoFlex Joint Support.

An aid to cavaliers suffering from arthritis is an elevated dog food bowl. The Ergo Feeder (right) is an example


Research News

January 2024: Cavaliers ranked fourth among 84 cases of immune-mediated polyarthritis cases in one UK hospital study. Dr. Judith Cruzado PerezIn a January 2024 article, UK researchers (Judith Cruzado Perez [right], Victoria Travail, Valerie Lamb, Darren Kelly) reviewed 84 cases of canine immune-mediated polyarthritis at one UK animal hospital during the years 2011-2021. Dogs with neutrophilic inflammation in 2 or more joints were included. Three of the dogs (3.5%) were cavalier King Charles spaniels. The object of the study was to describe the patients, their symptoms, physical condtions, treatments, and outcomes. They concluded that "IMPA carries a fair prognosis, but relapses occur in many cases and euthanasia due to relapsing or refractory disease is not uncommon."

May 2022: Cavaliers were the second most prevalent breed in a UK study of dogs with immune-mediated polyarthritis (IMPA). Dr. Lucy A. BarkerIn a May 2022 article, UK veterinary researchers Lucy A. Barker (right), S. McManus, S. Adamantos, and V. Black examined the medical records of 58 dogs diagnosed with idiopathic non-erosive immune-mediated polyarthritis (IMPA) to determine the clinical role which proteinuria may play in IMPA and to determine if proteinuria resolves on the treatment of the underlying IMPA. The most common affected breed was the cocker spaniel at 8.6%, followed by the cavalier King Charles spaniel at 7%. They found that proteinuria was a common abnormality in IMPA-affected dogs being studied and appears to frequently resolve on the treatment of the underlying disease.

November 2016: Cavaliers were 15+% of dogs with erosive immune-mediated polyarthritis (IMPA). Left carpus of CKCSIn a November 2016 article, a team of Wisconsin and Michigan researchers (Magen L. Shaughnessy, Susannah J. Sample, Carter Abicht, Caitlin Heaton, Peter Muir)  studied the clinical records of 79 dogs diagnosed with immune-mediated polyarthritis (IMPA). Of those 79 dogs, 13 had erosive IMPA, of which, two were cavalier King Charles spaniels. The 13 affected dogs had erosive lesions in their carpal joints. The estimated median synovial fluid lymphocyte count for dogs with erosive IMPA was significantly greater than that for dogs with nonerosive IMPA. Results indicated erosive IMPA most commonly affected the carpal joints of middle-aged small-breed dogs. (See left carpus of an 8-year-old spayed female Cavalier King Charles Spaniel with subjectively moderate subchondral bone lysis accompanied by severe synovial swelling -- in x-ray at right.)



Veterinary Resources

Idiopathic, non-infectious, non-erosive arthritis in a bitch. C.R. Hutchings, G.A. Verkerk, K.J. Kissling. New Zealand Vet. J. 1980;28(5). Quote: A 2 1/2-year-old Cavalier King Charles Spaniel bitch was examined because of recurring episodes of lameness and joint swelling over a period of 2 years. Clinical examination, radiography, serology, joint-fluid analysis and histopathology of the joint capsule led to a diagnosis of idiopathic, non-infectious, non-erosive arthritis. Combination therapy with prednisolone, cyclophosphamide and azothioprine produced a rapid improvement in the dog's condition. The features of this disease and its relationship to rheumatoid arthritis and systemic lupus erythematosis are discussed.

Immune-based non-erosive inflammatory joint disease of the dog. 3. Canine idiopathic polyarthritis. David Bennett. J. Sm. Anim. Pract. October 1987; doi: 10.1111/j.1748-5827.1987.tb01316.x. Quote: The features of 67 cases of canine idiopathic polyarthritis are described. Idiopathic polyarthritis includes cases of non-infective polysynovitis which cannot be classified into more defined groups. It most often affects young adult dogs, and pyrexia, inappetence and lethargy are exhibited as well as lameness. Radiography usually shows soft tissue changes. Four types are identified according to certain associations; [34 dogs with] Type I (uncomplicated), [19 dogs with] Type II (infection elsewhere in the body), [8 dogs with] Type III (gastro-intestinal disease) [including one cavalier King Charles spaniel (12.5%)] and [6 dogs with] Type IV (neoplastic disease elsewhere in the body). ... Type III (enteropathic arthritis): polyarthritis associated with gastro-intestinal disease; eg, gastro-enteritis, ulcerative colitis. ... In Type III cases the gastro-intestinal disease was treated usually with antibiotics and kaolin preparations. ... Prednisolone was the drug of choice in the Type I cases and was also used in Types II and III to help resolve the joint inflammation. ... If the animal relapsed at a later date, the dosage regime was repeated. In some cases, especially where relapses were common [including the CKCS], cytotoxic drugs were used; ie, cyclophosphamide or azathioprine.

Micronized/ultramicronized palmitoylethanolamide displays superior oral efficacy compared to nonmicronized palmitoylethanolamide in a rat model of inflammatory pain. Daniela Impellizzeri, Giuseppe Bruschetta, Marika Cordaro, Rosalia Crupi, Rosalba Siracusa, Emanuela Esposito, Salvatore Cuzzocrea. Neuroinflammation. August 2014; doi: 10.1186/s12974-014-0136-0. Quote: Background: The fatty acid amide palmitoylethanolamide (PEA) has been studied extensively for its anti-inflammatory and neuroprotective actions. The lipidic nature and large particle size of PEA in the native state may limit its solubility and bioavailability when given orally, however. Micronized formulations of a drug enhance its rate of dissolution and reduce variability of absorption when orally administered. The present study was thus designed to evaluate the oral anti-inflammatory efficacy of micronized/ultramicronized versus nonmicronized PEA formulations. Methods: Micronized/ultramicronized PEA was produced by the air-jet milling technique, and the various PEA preparations were subjected to physicochemical characterization to determine particle size distribution and purity. Each PEA formulation was then assessed for its anti-inflammatory effects when given orally in the carrageenan-induced rat paw model of inflammation, a well-established paradigm of edema formation and thermal hyperalgesia. Results: Intraplantar injection of carrageenan into the right hind paw led to a marked accumulation of infiltrating inflammatory cells and increased myeloperoxidase activity. Both parameters were significantly decreased by orally given micronized PEA (PEA-m; 10 mg/kg) or ultramicronized PEA (PEA-um; 10 mg/kg), but not nonmicronized PeaPure (10 mg/kg). Further, carrageenan-induced paw edema and thermal hyperalgesia were markedly and significantly reduced by oral treatment with micronized PEA-m and ultramicronized PEA-um at each time point compared to nonmicronized PeaPure. However, when given by the intraperitoneal route, all PEA formulations proved effective. Conclusions: These findings illustrate the superior anti-inflammatory action exerted by orally administered, micronized PEA-m and ultramicronized PEA-um, versus that of nonmicronized PeaPure, in the rat paw carrageenan model of inflammatory pain.

Nerve Growth Factor: A Focus on Neuroscience and Therapy. Luigi Aloe, Maria Luisa Rocco, Bijorn Omar Balzamino, Alessandra Micera. Curr. Neuropharmacol. May 2015; doi: 10.2174/2F1570159X13666150403231920 Quote: Nerve growth factor (NGF) is the firstly discovered and best characterized neurotrophic factor, known to play a critical protective role in the development and survival of sympathetic, sensory and forebrain cholinergic neurons. NGF promotes neuritis outgrowth both in vivo and in vitro and nerve cell recovery after ischemic, surgical or chemical injuries. Recently, the therapeutic property of NGF has been demonstrated on human cutaneous and corneal ulcers, pressure ulcer, glaucoma, maculopathy and retinitis pigmentosa. NGF eye drops administration is well tolerated, with no detectable clinical evidence of systemic or local adverse effects. The aim of this review is to summarize these biological properties and the potential clinical development of NGF.

Clinical features and pathological joint changes in dogs with erosive immune-mediated polyarthritis: 13 cases (2004–2012). Magen L. Shaughnessy, Susannah J. Sample, Carter Abicht, Caitlin Heaton, Peter Muir. JAVMA. November 2016;249(10):1156-1164. Quote: Objective: To evaluate the clinical features and pathological joint changes in dogs with erosive immune-mediated polyarthritis (IMPA). Design: Retrospective case series. Animals: 13 dogs with erosive IMPA [including two cavalier King Charles spaniels (15.4%)] and 66 dogs with nonerosive IMPA. Procedures: The medical record database of a veterinary teaching hospital was reviewed to identify dogs with IMPA that were examined between October 2004 and December 2012. Left carpus of CKCSFor each IMPA-affected dog, information extracted from the medical record included signalment, diagnostic test results, radiographic findings, and treatments administered. Dogs were classified as having erosive IMPA if review of radiographs revealed the presence of bone lysis in multiple joints, and descriptive data were generated for those dogs. All available direct smears of synovial fluid samples underwent cytologic evaluation. The synovial fluid total nucleated cell count and WBC differential count were estimated and compared between dogs with erosive IMPA and dogs with nonerosive IMPA. Results: 13 of 79 (16%) dogs had erosive IMPA. Dogs with erosive IMPA had a mean ± SD age of 7.1 ± 2.4 years and body weight of 8.3 ± 3.4 kg (18.3 ± 7.5 lb). All 13 dogs had erosive lesions in their carpal joints. (See left carpus of an 8-year-old spayed female Cavalier King Charles Spaniel with subjectively moderate subchondral bone lysis accompanied by severe synovial swelling -- in x-ray at right).The estimated median synovial fluid lymphocyte count for dogs with erosive IMPA was significantly greater than that for dogs with nonerosive IMPA. All dogs received immunosuppressive therapy with leflunomide (n = 9), prednisone (3), or prednisone-azathioprine (1). Conclusions & Clinical Relevance: Results indicated erosive IMPA most commonly affected the carpal joints of middle-aged small-breed dogs. Further genetic analyses and analysis of lymphocyte-subsets are warranted for dogs with erosive IMPA.

Point prevalence and clinical course of proteinuria in dogs with idiopathic non-erosive immune-mediated polyarthritis. L. Barker, S. McManus, S. Adamantos, V. Black. J. Sm. Anim. Pract. May 2022; doi: 10.1111/jsap.13503. Quote: Objectives: To describe the point prevalence and clinical course of proteinuria in dogs diagnosed with idiopathic non-erosive immune-mediated polyarthritis. Materials and Methods: Cases presenting to a single referral centre with a diagnosis of idiopathic non-erosive immune-mediated polyarthritis were retrospectively recruited from January 2009 to August 2018. Data including signalment, urinalysis, clinicopathological results, cytology from arthrocentesis, treatment and long-term follow-up were analysed. Dogs were defined as: non-proteinuric (UPC <0.2), borderline proteinuric (UPC 0.2-0.5) or overtly proteinuric (UPC >0.5). Results: Fifty-eight dogs met the inclusion criteria. ... Presenting breeds included cocker spaniel (n=5), Cavalier King Charles spaniel (n=4) [7%], Labrador retriever (n=4), whippet (n=4), springer spaniel (n=3), Chinese crested (n=2), corgi (n=2), Jack Russell terrier (n=2), English pointer (n=2), and 13 dogs of mixed breeds and one each of 18 other breeds. ... Twenty-two dogs were overtly proteinuric (38%), eight dogs were borderline proteinuric (14%) and 28 dogs were non-proteinuric (48%). Repeated urinalysis was performed in nine of 12 dogs with UPC greater than 2.0. The UPC decreased in all nine dogs, with the UPC decreasing to less than 0.5 in 44% of dogs. A greater than 50% decrease in UPC was noted in 44% of dogs, despite seven of nine (77%) receiving prednisolone as either monotherapy or in conjunction with an adjunctive immunosuppressive medication. Clinical Significance: Proteinuria was common in this cohort of dogs diagnosed with primary idiopathic non-erosive immune-mediated polyarthritis. The use of prednisolone does not appear to be contraindicated in proteinuric dogs with idiopathic non-erosive immune-mediated polyarthritis.

Librela (Beransa) – Wonder Drug Or Disaster In The Making? Edward Bassingthwaighte. Dogs Naturally. October 2023. Quote: In my professional opinion, there is no way that Librela should ever be considered as a first treatment or intervention for arthritis in dogs.

Canine immune-mediated polyarthritis: A review of 84 cases in the UK between 2011 and 2021. Judith Cruzado Perez, Victoria Travail, Valerie Lamb, Darren Kelly. Vet. Med. & Sci. January 2024; doi: 10.1002/vms3.1306. Background: Immune-mediated polyarthritis (IMPA) is a well-recognised disease in dogs, but studies evaluating the response rates, relapse rates and long-term outcomes are scarce. Objectives: To provide an updated description of the signalment, clinical signs, clinico- pathological findings, distribution between subgroups, rates of response and relapse and long-term outcome of 84 dogs diagnosed with IMPA at a single referral hospital. Methods: Dogs diagnosed with IMPA between January 2011 and December 2021 were identified. Dogs with neutrophilic inflammation in ≥2 joints were included. Cases with <1 month of follow-up, or those missing pertinent data, were excluded. Results: A total of 84 cases were included. ... Cocker spaniels (9/84), Labrador retrievers (6/84), Border col- lies (6/84), Springer spaniels (5/84), Cavalier King Charles spaniels (3/84), Boxers (3/84), German shepherds (2/84), West Highland White terriers (2/84) and Golden retrievers (2/84) were included. The remain- ing cases (32/84) were represented by one individual of different pure breeds. ... An initial response was achieved in 77/84 (92%) cases. Of the cases that initially responded, 37/77 (48%) suffered at least one relapse and 18/77 (23%) suffered multiple relapses. Indefinite treatment was recom- mended in 17/84 (20%) cases. Of the 70 dogs for which at least 12 months of follow-up data were available, 12/70 (17%) were euthanised due to IMPA or for unknown reasons. Conclusion: IMPA carries a fair prognosis, but relapses occur in many cases and euthanasia due to relapsing or refractory disease is not uncommon.