When we’re talking about the overlap between arthritis and meningitis, we are actually talking about a specific type of disease process. This isn’t about the old-age, wear-and-tear arthritis we’re all familiar with. We mean immune-mediated polyarthritis, a condition in which the body’s own immune system attacks its joints. This condition can overlap with another autoimmune condition in dogs known as steroid-responsive meningitis-arteritis (SRMA). 

These are complicated disease processes, so we’re going to take the time to explore each one in turn. We’ll also look at the reason they may occur at the same time and what the treatment options are if your pet is diagnosed.  

What is immune-mediated polyarthritis (IMPA) in dogs? 

Immune-mediated polyarthritis (IMPA) is a disorder of the immune system. The immune system is usually great at fighting off infections and keeping us healthy. However, in autoimmune conditions, the immune system goes rogue and starts attacking the body’s own cells, in this case the tissues within the joints. This can sometimes be triggered by other illness elsewhere in the body. Classically, IMPA can be categorised into four main types as follows:  

  • Type I – Idiopathic – an underlying cause is not identified  
  • Type II – Secondary to a non-joint infection (e.g. a urinary tract infection or respiratory infection) 
  • Type III – Secondary to chronic gastrointestinal disease like inflammatory bowel disease 
  • Type IV – Secondary to neoplasia (cancer) 

However, some vets simplify things further and just classify the condition as primary IMPA (‘idiopathic’) or secondary (‘reactive’) IMPA. Note that drug reactions are another possible cause of IMPA. 

Because this condition can occur secondary to other health conditions, some of which are more common with advancing age, the average age for a dog to develop IMPA has been reported to be around 5.5 years. However, dogs younger and older than this can be affected. 

What are the symptoms? 

The symptoms of IMPA can vary, but commonly include – 

  • A stiff or stilted gait – often described as ‘walking on eggshells’ 
  • Lameness which may be shifting (affecting different limbs at different times) 
  • Reluctance to walk and exercise 
  • Swollen, painful joints 
  • Back pain 
  • Fever 
  • Reduced appetite 
  • Vomiting or diarrhoea 

How is IMPA diagnosed in dogs? 

We can’t just presume that every dog presenting with painful swollen joints has immune-mediated disease. It’s important to rule out other causes of joint pain including osteoarthritis and bacterial, parasitic, or viral infections e.g. tick-borne diseases. 

Your vet will start by doing a physical examination and taking a history from you. If they suspect a joint issue they may recommend the following tests: 

  • Blood samples – Biochemistry and haematology help identify features of inflammation and infection, as well as checking other markers of health such as kidney and liver values. 
  • Urinalysis – A urine sample can be useful to check for other possible illness like urinary tract infections, as well as checking your pet’s kidney function. 
  • Infectious disease screening – the treatment for dog’s suffering from infectious disease will be very different to those that have an immune-mediated condition. So, it’s usually recommended to screen and rule these out. 
  • Diagnostic imaging – X-rays can be used to assess joint damage as well as looking for other health conditions that could be contributing to the immune system malfunction, such as underlying cancer processes. 

If an underlying cause for your dog’s symptoms is found, then this will need to be treated. 

If no disease is found, your vet may recommend taking samples from the joints themselves. Arthrocentesis involves inserting a needle into a joint space to retrieve fluid. This is done under sedation or anaesthetic. The collected fluid can then be sent off for – 

  • Culture – Culturing the fluid can help to grow and identify any bacteria present. If this is positive, then septic arthritis is diagnosed rather than IMPA. 
  • Cytology – Looking at joint fluid sample under the microscope can identify the presence of inflammatory cells. A sample that contains neutrophils (a type of white blood cell) but no infectious agents like bacteria can raise suspicions of IMPA.  Many white blood cells and neutrophils, along with a positive culture, would indicate an infected joint (septic arthritis). Few white blood cells present may indicate a different disease process, like osteoarthritis.  

What is steroid-responsive meningitis-arteritis (SRMA) in dogs? 

Meningitis refers to inflammation of the meninges, which are the thin tissues covering the brain and spinal cord. In people, meningitis usually occurs due to bacterial or viral infection. However, thanks to vaccinations, this is less common in dogs. 

Instead, we more frequently diagnose immune-mediated meningitis, in particular steroid-responsive meningitis-arteritis (SRMA). In this condition, the arteries in the meninges are affected. This condition is not contagious to other dogs, as, again, it is the animal’s own immune system causing the problem and attacking blood vessel tissues in the body.  

What dogs are commonly affected by SRMA? 

The exact trigger for SRMA is unknown. It is most common in younger dogs, less than two years of age. Any breed can be affected, but it occurs more often in some than others meaning there may be a genetic component to this disease. Breeds more at risk include Bernese Mountain dogs, Beagles, Boxers, and Weimeraners.  

What are the symptoms? 

Symptoms can vary and may be vague, but usually include:

  • Spinal pain – your dog may appear hunched or react when their back is touched 
  • Neck pain – most noted during an examination, when the head is bent down towards the chest 
  • Pain when the tail is manipulated 
  • Stiff gait 
  • Fever 
  • Reduced appetite 
  • Lethargy 

How is SRMA diagnosed in dogs? 

There is no single confirmatory test for SRMA, and it is usually diagnosed through a process of elimination. Other causes of fever, neck and back pain need to be ruled out first. To do this, your vet will need to run some test: 

  • Blood tests – Blood samples help to check for inflammation and infection. As well as routine biochemistry and haematology, a specific blood test called C-reactive protein may be run. This is an acute phase protein which can be elevated in SRMA cases, and to varying degrees with some other health conditions too. 
  • Urinalysis – A urine sample can be useful to check for other possible illnesses like urinary tract infections, as well as checking your pet’s kidney function. 
  • Infectious disease screening – the treatment for dog’s suffering from infectious disease will be very different to those that have an immune-mediated condition. So, it’s usually recommended to try and rule these out. 
  • Diagnostic imaging – X-rays can be used to screen for some causes of neck and spinal pain, but advanced imaging can give more detailed information, helping to rule out conditions like intervertebral disc disease (IVDD) and syringomyelia. 
  • Cerebrospinal fluid analysis – A spinal tap is performed to analyse cerebrospinal fluid. Much like the joint samples we discussed before in IMPA, fluid from the spinal column can be cultured to look for infection as well as being examined under the microscope. In cases of SRMA, no infectious agents are found, and the fluid often contains high levels of protein and white blood cells, especially neutrophils, associated with inflammation. Red blood cells from secondary haemorrhage may also be seen. 

Why do IMPA and SRMA seem to happen at the same time? 

Both conditions arise due to an underlying immune system dysfunction and share similar symptoms like fever, lethargy, and reduced mobility. 

In SRMA, the immune system attacks blood vessels in the meninges, but vessels within the joints are sometimes affected too. This can give rise to joint pain, join swelling, and lameness in a dog with SRMA. In this case, their polyarthritis could be considered part of their SRMA condition. 

In dogs that are suffering from IMPA, there are high levels of circulating immune complexes in their bodies and widespread shifts in neutrophils. These inflammatory changes can end up affecting the meninges as well as the joints. In effect, problems in the central nervous system occur due to a spillover of IMPA. Plus, as IMPA affects joints, the joints of the spinal cord can be affected, causing pain. 

So, in some cases, rather than IMPA and SRMA occurring at the same time, it could just be a variation in the degree to which each condition is expressing itself. Overlapping symptoms between the two conditions can occur, confusing the clinical picture. 

Studies looking at the overlap between the two immune-mediated disorders are lacking, so it’s difficult to know the exact figures for dogs that have both IMPA and SRMA at the same time. One paper states that  ‘Occasionally, canine SRMA is accompanied with immune-mediated polyarthritis’. They go on to reference different sources describing different levels of reported frequency. The most recent one that it quotes suggested that only 9% of SRMA cases also had IMPA. 

This 2023 study has explored ways of differentiating the two conditions with the use of C-reactive protein levels, but more work is needed. 

So while IMPA and SRMA (arthritis and meningitis) can occur at the same time, each disease shares similar features that clinically overlap. It looks like the majority of cases may just have one condition or the other. Which figures, when we look at the difference in typically affected age groups of the two conditions. 

What is the treatment for IMPA and SRMA? 

Treatment for both conditions is actually very similar – immunosuppressive therapy which you will need to administer regularly at home after initial supportive care. 

A course of high-dose prednisolone (steroids) is often prescribed to suppress the dog’s immune system. This is usually a tapering regime, meaning the exact doses your pet needs to take will decrease gradually over time. 

Exact doses and timeframes may vary, but most protocols (e.g. from VIN (Veterinary Information Network)) stress the importance of starting with a very high dose, then tapering down gradually, hoping to be able to stop therapy after 5-7 months if all goes well. 

Although many pets respond well, it’s important to recognise that relapses can occur in both conditions. Also, they can suffer from the side effects of high-dose steroids during their treatment period, which can include increased thirst and appetite, increased urination, depression, lethargy, and muscle weakness. Sometimes other immunosuppressive medications are also needed. 

In the management of IMPA, controlling any underlying causative disease processes is also an important part of the treatment. In the case of drug reactions, some cases of IMPA may resolve by themselves without immunosuppressive treatment. 

The usual course of immunosuppressive treatment for most dogs can last several months, and your vet will advise regular check-ups during this time. They may also use C-reactive protein blood tests as a monitoring tool, especially in SRMA, to check that levels of this inflammatory marker are falling. 

If you have any questions about your dog’s treatment, then don’t hesitate to ask your vet. 

Summary 

IMPA and SRMA are both immune-mediated diseases that share very similar clinical symptoms, including changes in mobility, fever, and lethargy. We know that a dog with SRMA can have joint pain as well as spinal pain, and a dog with IMPA can have back pain as well as classic joint pain. This can make it look like the affected pet has both conditions at the same time. 

While it is definitely possible for a dog to have both SRMA and IMPA together, more studies are needed into this. But rest assured, your vet will recommend diagnostics to help diagnose what it is going on and tailor a treatment plan for your pet accordingly.