86 | How to ACTUALLY use your skills when caring for dogs with IMPA

PodcastImmune-mediated DiseaseMusculoskeletal Disease
Written By Laura Jones

We’re chatting all about a rare but intensive disease today: immune‑mediated polyarthritis, or IMPA.

 

When I worked in general practice, I had no idea IMPA was even a thing. Until I started in referral as a brand new medicine nurse, and suddenly had a very lame, very pyrexic black labrador to care for. I was completely confused why we were seeing a lameness case - until we tapped the joints, found inflammation, and I learned just how much damage the immune system can do.

My patient needed a LOT of nursing - recumbency management, potent analgesia and a lot of supportive care. And through looking after him, I learned just how vital nurses are in managing this condition.

In today’s episode, we’ll cover:

  1. What IMPA is and how it develops

  2. The signs we tend to see in patients with it

  3. How we accurately diagnose and differentiate IMPA

  4. How we successfully treat and manage it

  5. The skills we can use to support these patients - both in the hospital, and long-term.

So let’s jump straight in.

Ok. What on earth is immune-mediated polyrthritis (IMPA)!?

As the name suggests, immune‑mediated polyarthritis (or polyarthropathy) is a condition in which the immune system attacks the joints, causing autoinflammation.

There are actually two forms of IMPA: erosive and non-erosive.

Erosive IMPA is otherwise known as rheumatoid arthritis, and is characterised by joint inflammation and erosion. In these patients, the bone and cartilage in the joints become damaged by rheumatoid factor and T-lymphocyte-mediated immune pathways. As a result, the articular cartilage often develops lytic, so-called ‘punched-out’ lesions, almost like dimples on a gold ball. This form of IMPA is seen less commonly, and is usually diagnosed in older, small-breed dogs. Additionally, certain types of erosive IMPA exist in specific breeds, such as greyhounds.

Non-erosive IMPA is by far the most common form of the disease we see. In these patients, immune complexes are deposited in the synovial membranes, where they trigger joint inflammation. We usually see non-erosive IMPA in young, large-breed dogs and it typically affects the distal joints; particularly the carpi, tarsi, elbows and stifles. It can affect cats, though rarely.

Because non-erosive IMPA is the disease you’re most likely to see in practice, I’m going to focus on that for the rest of this episode.

So there are actually four subtypes of IMPA; it can be classified as type I, type II, type III or type IV.

Type I is the most common type we see. This is idiopathic or primary IMPA, where no specific trigger for the immune reaction is identified. Type II is IMPA associated with infection (e.g. Lyme disease, as we discussed in episode 85), type III is associated with gastrointestinal or hepatic disease, and type IV is associated with neoplasia.

Identifying whether we’re dealing with primary (type I) IMPA or an associative form of IMPA is essential, since it’ll guide our decisions on treatment and nursing care.

Ok, so that’s what IMPA is. But how do these patients present to us?

These patients have varied and sometimes subtle clinical signs. Many patients present with pyrexia - in fact, IMPA is one of the leading causes of pyrexia of unknown origin in dogs, with at least 50% of IMPA patients presenting with pyrexia.

Many dogs present with ambulatory changes, including a stiff or stilted gait, reluctance to walk and shifting leg lameness. Patients often appear as though they are ‘walking on eggshells’ and joints are often painful when they’re palpated or manipulated during examination.

Some patients will have obvious joint effusion or soft swelling on examination, though this may not be apparent in all patients with IMPA. 

Aside from musculoskeletal signs, these patients generally present with signs of systemic illness due to their inflammation and pyrexia. Dogs with IMPA are often lethargic, depressed, inappetant or completely anorexic.

Depending on the severity of the joint pain and inflammation, patients may present collapsed and unable to walk, or with more subtle signs - so examining patients carefully, and not excluding the condition based on an absence of joint swelling, for example, is vital.

Many young dogs <8 months old with these signs have concurrent metaphyseal osteopathy. This is an inflammatory bone disorder seen in rapidly-growing, large breed dogs. This is common in breeds such as Great Danes, Irish Setters, Weimeraners and Boxers, though any large breed puppy can be affected. It causes the same signs as IMPA.

So you think your patient has IMPA. How will we diagnose them?

Diagnosing IMPA can be challenging and these patients require several diagnostic procedures, many of which we can perform or assist with as veterinary nurses and technicians. Investigations include bloodwork, urine analysis, diagnostic imaging and arthrocentesis, or joint taps, with the goal to confirm joint inflammation, and rule in or out associative causes.

Let’s start by looking at bloodwork.

Patients will have a biochemistry and haematology, which often shows inflammatory changes, particularly to the leukogram. 

We’ll also add a C-reactive protein (or CRP) test to the biochemistry panel; CRP is a marker of inflammation, and is often very high in IMPA patients. With successful treatment, we should see the CRP level reduce over time, and it’s often used to monitor response to ongoing treatment as a result.

Depdending on how severely anorexic, dehydrated, etc our patient is, we’ll see varying changes to things like electrolytes and PCV; these should normalise as we restore hydration and provide supportive treatment.

Alongside CRP testing, ruling out infectious diseases is essential. As we chatted about in episode 85, tick-borne diseases commonly cause similar signs, so a 4Dx test should be performed as a minimum.

What about urine analysis?

We often perform a UA in these patients to look for evidence of infection or other inflammation/disease acting as a potential trigger. Ideally, this would be a cystocentesis sample, particularly if you plan to culture it.

And then we’ve got diagnostic imaging.

These patients generally have X-rays of the affected limbs and the thorax, and an abdominal ultrasound +/- sampling of any abnormalities found on imaging. This is important to determine the severity of joint inflammation or erosion (in erosive cases), and look for underlying triggers such as tumours or GI/hepatic changes.

And finally, we need to take samples of those joints.

Arthrocentesis is performed under deep sedation or general anaesthesia. At least 4 joints (usually both carpi, both tarsi and either elbows or stifle, depending on the degree of joint effusion) are sampled, collecting small volumes of synovial fluid for analysis.

This fluid is submitted for cytology and culture, with fresh synovial fluid smears performed, and spare fluid collected either in a plain sterile tube, or a blood culture bottle.

Synovial fluid is usually viscous, sticky in consistency, and clear; in IMPA patients, the joints generally contain larger volumes of turbid, liquid fluid. This fluid is highly cellular, high in protein, and non-septic. If you look at it under the microscope (which, nurses, you should if you don’t already!) you’ll see lots of neutrophils without bacteria or other evidence of infection.

Once you’ve ruled out infection, neoplasia, triggering disease or any other specific cause, you’re left with a diagnosis of idiopathic or primary IMPA.

Once your patient’s IMPA is confirmed, we need to think about treatment.

Like lots of our immune-mediated diseases, our first-line treatment is immunosuppression. We need to dampen down that immune response so that it stops identifying its own joints as harmful, and attacks them.

Our first drug is our favourite: prednisolone. It’s often started at higher doses (such as 2mg/kg/day) to interrupt the immune response, and then doses adjusted and other agents added depending on the patient’s ongoing signs. In larger dogs, doses are often calculated based on body surface area, rather than weight, to improve accuracy.

We usually see these patients improve quickly, with pyrexia, lameness and joint effusion often starting to resolve in the initial 24-48 hours after treatment.

Unfortunately, many patients will not stabilise on prednisolone alone. In addition, we know that high doses of pred come with side-effects, such as marked PUPD, that can be detrimental to the patient. In these cases, additional immunosuporessive medications (aka ‘second agents’) are added. Examples include lefunomide, azathioprine, cyclosporine, or methotrexate. Many of these drugs are cytotoxic and require special handling and management.

In a recent review of UK 84 dogs with IMPA:

  • 92% initial response

  • 48% had at least one relapse

  • 23% relapsed multiple times

  • 20% required indefinite treatment

  • 17% were euthanised due to refractory disease or other reasons

So we know we’ll be treating these patients for quite some time, often with multiple agents, until their clinical signs and CRP levels improve.

Aside from immunosuppression, the rest of our treatment is supportive.

These patients need good quality, multimodal analgesia - avoiding NSAIDs since steroids will be indicated. Methadone (or fentanyl in severe cases), lidocaine, ketamine and paracetamol are good options for these patients, depending on the severity of their pain.

Alongside analgesia, maintaining hydration and nutritional status is essential in these patients. Many patients are dehydrated or hypovolaemic on presentation, and require fluid therapy alongside careful monitoring of fluid balance. Supportive nutrition is also provided until the patient meets their calorie needs consistently - and we’re ideally placed as nurses and technicians to manage this.

Treating these patients isn’t easy, and nursing them often isn’t, either.

These patients need a LOT of support, but with that comes a ton of opportunity for us to use our nursing skills. To give great care to your IMPA patients, prioritise pain management, environmental adjustments to improve comfort, careful handling, nutrition and hydration, elimination management, recumbency care, and ongoing support.

Assess their pain and advocate for multimodal analgesia. Calculate the CRI. Place the urinary catheter if they’re not walking. Even assist with or perform arthrocentesis if you’re legally able to!

And, once the patient improves, our nursing care doesn’t end - it’s an important part of their ongoing care.

Clients need to understand that relapses are common and treatment can be long term. They should know how to assess pain at home, how to manage their dog’s exercise regime, what medication side-effects to look out for, and how often they’ll need to come back. And nurses are ideally placed to support patients, and their families, with that long-term care.

So there you have it! A quick tour of all-things IMPA, and the impact it has on our patients. IMPA is a deceptively subtle disease, with signs ranging from mild lameness to serious systemic illness. And whilst it depends on the type of IMPA our patient has, most patients will require significant immunosuppression alongside intensive supportive care, which is where we really come into our own, and get to show off our skills.

Did you enjoy this episode? If so, I’d love to hear what you think. Take a screenshot and tag me on Instagram (@vetinternalmedicinenursing) so I can give you a shout-out and share it with a colleague who’d find it helpful!

Thanks for learning with me this week, and I’ll see you next time!


References and Further Reading

Laura Jones
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85 | Tick-borne disease in dogs: what do vet nurses NEED to know?