Vets, Test Yourself with our Free Neurology CPD Case Study!
By Rebecca MacMillan BVetMed BSAVA PGCertSAM MRCVS
Are you looking for free neurology CPD? Walk through this veterinary neurology case study with Dr Rebecca MacMillan and see if you can work out what’s wrong with the dog. When you’re finished, don’t forget to log your CPD on 1CPD and reflect on what you’ve learned – we’ve got some CPD reflection tips for you too.
History and Presenting Problem
A 3-year-old female neutered Labrador retriever presents to your practice because, in the past week, she has started ‘bringing up her food’. The owner also mentions that her bark has changed recently and that she is drooling more than usual. They also state that their dog seems a bit quieter and weaker than usual. On further questioning the owner reports that there is no abdominal effort when she is bringing her food up, and what she produces is largely undigested. This makes you suspicious that the dog is regurgitating rather than vomiting.
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Your Clinical Exam
Your physical examination reveals a normal mentation but a decreased palpebral reflex. Mucous membranes are pale pink with a capillary refill time of 1.5 seconds. The dog’s heart rate is 112 beats per minute, and they have a respiratory rate of 36 breaths per minute. Abdominal palpation is unremarkable and rectal temperature is 38.8C. The dog’s peripheral lymph nodes are within normal limits and there is no evidence of joint pain. You decide to trot the dog up and down outside the practice to assess her mobility. While she starts well and seems keen to walk, she soon becomes weak and struggles.
What is your problem list for this dog? Try to list each of the problems you’ve spotted in your history and clinical exam – this will help make sure you don’t miss any potential differential diagnoses later.
Answer – Problem List
Regurgitation
Exercise induced weakness
Drooling
Change in vocalisation
Subdued demeanour
What are some of your differential diagnoses for each of these patient’s problems? List your differential diagnoses for each problem. Your list should be quite long!
Answer – Differential Diagnosis List
Here are a few possible differentials (you may have come up with additional ones):
Regurgitation – primary (idiopathic) megaoesophagus, secondary megaoesophagus, oesophageal stricture, neoplasia, foreign body and granuloma
Exercise-induced weakness – anaemia, cardiac disease, myasthenia gravis, respiratory disorders, myopathies, polyneuropathies and orthopaedic disease.
Drooling – nausea, dental disease, neoplasia, foreign body, toxicity, difficulty swallowing (e.g. myasthenia gravis) and stress
Change in vocalisation – overuse/too much barking, laryngitis, laryngeal paralysis, myasthenia gravis, degenerative myelopathy and neoplasia
Subdued demeanour – non-specific finding, could be due to multiple underlying health issues
If you came up with some of those, well done! Now, you can see some of our differential diagnoses are possible for many of our problems, which makes them more likely – although we can’t rule out multiple diseases causing this problem list.
What diagnostic tests do you propose to do? How will you start to sort the likely diagnoses from the less likely ones?
Answer – Diagnostic Tests
It is sensible to run a baseline biochemistry, electrolytes and haematology, to screen for any indications of underlying disease processes, anaemia or markers of inflammation. In the case of this dog, routine blood work (including T4) was unremarkable.
What next?
Based on this and your physical examination (and the signalment of a large breed dog) it would be appropriate for you to do an anti-AChR antibody titre test. This test screens for acquired myasthenia gravis, an immune-mediated condition caused by antibodies which are directed towards the acetylcholine receptors found at the nerve-muscle junction. However, there is only one laboratory, located at the University of California (San Diego), that can run it. This means there can be a delay in receiving the test results, plus the test can also be quite expensive. However, it is accurate for diagnosing 98% of myasthenia gravis cases.
Unfortunately, the other test for diagnosing myasthenia gravis, the ‘Tensilon test’ has limited availability. This test involves giving an intravenous injection of edrophonium chloride (brand name Tensilon®) which is a short-acting anticholinesterase. This helps to strengthen messages from nerve to muscle, by allowing acetylcholine to accumulate in the neuromuscular junction. Dogs with myasthenia gravis should respond rapidly, going from weak to able to exercise well shortly after receiving the injection. This gives a much faster diagnosis than the AChR test, but false negatives and positives can occur. The main issue is that edrophonium chloride is not being commercially manufactured at the time of writing, so this test is not widely available. You may wish to consult with a vet neurology specialist on this.
What other tests should you perform while waiting? In practice, there’s usually a delay on test results (not like in these online case studies, where results are immediate!). What other tests could you do while you’re waiting?
Answer – Further Tests
In suspected cases of myasthenia gravis, it is appropriate to perform thoracic radiographs or a CT scan. This helps to evaluate the presence of megaoesophagus, which is present in 85% of myasthenia gravis cases. It also allows us to screen for other pathology such as aspiration pneumonia which could be associated with megaoesophagus (inhalation of reflux material is a real risk in these dogs), as well as masses in the chest cavity. Thymomas are found in 3-4% of myasthenia gravis cases. If a thymoma is found, then surgical removal is advised.
The results of your diagnostic tests indicate that your patient has myasthenia gravis. A megaoesophagus has been identified, but there is no evidence of either aspiration pneumonia or a thymoma at this time.
Well done, you’ve got your diagnosis! What’s next?
What are the treatment options available for this dog?
Answer – Treatment Options
Dogs with myasthenia gravis have an excess acetylcholinesterase which is an enzyme that breaks down acetylcholine (an important nerve cell messenger). A drug is therefore required that inhibits this enzyme, prolonging the action of acetylcholine. The drug that is recommended for these patients is pyridostigmine bromide (brand name Mestinon®).
Corticosteroids, azathioprine or mycophenolate can also be used to suppress immune system activity.
However, myasthenia gravis resolves spontaneously in most patients, so therapy is only required to control symptoms until that time. Most dogs will not require ongoing treatment for this condition.
Some patients with myasthenia gravis can be very unwell, especially if they have secondary complications such as aspiration pneumonia. These animals will require aggressive care with intravenous fluids, antibiotics and oxygen therapy. Some animals could need a feeding tube if they are unable to eat without regurgitation. They may require hospitalisation until the point that their medication has started to work.
Luckily this isn’t the case for your patient but due to their megaoesophagus, extreme care will need to be taken with their feeding regime to avoid this from occurring.
How will you monitor your patient’s progress? Just because you’ve got a diagnosis and a treatment plan doesn’t mean it’s the end of the case – how frequently do you want to monitor this case? What sort of tests do you want to do?
Answer – Monitoring
You should be able to appreciate a notable improvement in your patients if they are responding well to therapy. This includes improved muscle strength and a resolution of their weakness. In addition to observing the dog, you should repeat chest radiographs every 4-6 weeks to check that their megaoesophagus is resolving. Acetylcholine receptor antibody levels can also be monitored every 8-12 weeks. This should reduce into the normal reference range once the dog has entered remission.
The prognosis for complete recovery of myasthenia gravis in dogs is good, within approximately 6-8 months. Generally, younger animals such as your 3-year-old labrador patient will carry a better prognosis than older animals that are more likely to have neoplasia and co-morbidities. However, aspiration pneumonia is the greatest risk in animals that have developed megaoesophagus and is the leading cause of death in these patients. Dogs with thymomas will also have a more guarded prognosis unless the mass can be completely removed alongside a resolution in their clinical signs.
Congratulations, you solved the free neurology CPD case study!
Don’t forget to log your CPD hours from reading this article. You might find our article on CPD reflection helpful!
If you enjoyed this neurology case study and want to find out more, then why not consider our Small Animal Neurology course? It’s an online veterinary certificate programme, leading you to a GPCert in Small Animal Neurology. Alternatively, if you enjoy your neurology interspersed with some other subjects, take a look at our Small Animal Medicine course!
References:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8478050/
https://veterinarypartner.vin.com/default.aspx?pid=19239&id=4951980
