I received an email about a case question. The author was asking about Myasthenia Gravis. She noted that there wasn’t anything on Myasthenia Gravis on Four Leg. So, here is my response and a bit of background on the disease.
Firstly, What is it?
Myasthenia Gravis (MG) is a relatively rare, long term condition and an autoimmune neuromuscular disease caused by circulating antibodies that block acetylcholine receptors at the postsynaptic neuromuscular junction, inhibiting the excitatory effects of the neurotransmitter acetylcholine on nicotinic receptors at neuromuscular junctions leading to fluctuating muscle weakness and fatigue. It is generalized muscle weakness and the most common muscles affected are muscles that control the eyes and eyelids, facial expressions, chewing, swallowing, and speaking, respiratory muscles can be affected and may require urgent intervention.
The Neuromuscular Junction
1. Presynaptic terminal
3. Synaptic vesicle
4. Nicotinic acetylcholine receptor
The muscular weakness can be localized or generalized, and usually is more proximal than distal. Eye and oropharyngeal muscles are often affected, but the distribution of muscle weakness is highly variable. Muscle weakness causes common symptoms of MG that include: fatigue, breathing difficulties, ptosis, problems with chewing and swallowing, and dysarthria. Myasthenic crisis is a complication of MG characterized by worsening of muscle weakness, resulting in respiratory failure that requires intubation and mechanical ventilation. MG and thymic tumours are frequently associated.
From a Rehab Perspective, I think these aspects are key to understanding:
- Weakness is typically least severe in the morning and worsens as the day progresses.
- Weakness is increased by exertion and alleviated by rest.
- Weakness progresses from mild to more severe over weeks or months, with exacerbations and remissions.
Without going down the path of diagnostics and medical management, let’s jump right into REHABILITATION.
- Low to Medium intensity physical training. It is important to avoid High Intensity exercise, as it will increase muscular weakness.
- Balance between physical activity and rest. Note: We cannot cure the weakness, but we can ensure that physical function is optimized.
- Balance training can help to improve function.
- Gradual resistance training might be of value. Aim to strengthen large proximal muscle groups (i.e. those around the hips and shoulders).
- General aerobic exercise is also valuable.
- Exercise should be done earlier in the day when the patient is at his/her best.
- If a patient is on medication, perform exercises a couple of hours after administration of medication (for best effects of exercise).
- Monitor the patient during exercise for worsening of MG symptoms (i.e. ptosis or facial or other weaknesses)
- Be aware of myasthenic crisis: Myasthenic crisis is defined as respiratory muscle weakness that is severe enough to necessitate intubation or delay extubation.
This is a ‘life-long management’ disease. As rehab practitioners, our role might be to identify red flags if a dog is in our care but not diagnosed with MG, we can help dogs to recover from myasthenic crises, and we can help to empower owners to discover the right amount of exercise for their dog using the tips above and some trial and error.
I’m afraid, I don’t have enough to do a whole video on the topic, but this is a wee little knowledge nugget to stash away in your brain for when you need it!
1. https://www.physio-pedia.com/Myasthenia_Gravis (accessed April 13, 2022)
2. Corrado, B, Giardulli B, Costa M. Evidence-based practice in rehabilitation of Myasthenia Gravis. A systematic review of the literature. J Funct Morphol Kinesiol. 5(4), 2020: 71