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How to diagnose myasthenia gravis with the Tensilon test in a dog | VETgirl Veterinary CE Videos

In this VETgirl online veterinary continuing education video, we demonstrate how to diagnose myasthenia gravis with a Tensilon test in a dog. Myasthenia gravis, a neuromuscular disorder affecting dogs (and rarely, cats), represents as a dysfunction of the neuromuscular junction. This patient presented for signs of generalized muscular weakness exacerbated by exercise, and was ultimately diagnosed with generalized myasthenia gravis.

In this video, you can see that this patient was profoundly weak, which worsened over time even with mild exercise to the point where he did not wish to walk any further. Other clinical signs that may be seen with myasthenia gravis include megaesophagus, pharyngeal paralysis, decreased palpebral reflex and, occasionally, laryngeal and facial weakness. Although historical findings and the physical examination may lead to a suspicion of myasthenia gravis, definitive diagnosis of acquired myasthenia gravis should be confirmed by testing serum antibodies against acetylcholine receptors. This test has a 98% sensitivity in dogs affected by the generalized form of the disease.

In patients that are clinical, another test to consider is the Tensilon test. Edrophonium is a fast-acting anticholinesterase drug that is injected intravenously. As seen in this video, edrophonium is injected and the patient quickly becomes more mobile and active. This drug works by prolonging the acetylcholine life in the synaptic space and allowing it to attach to functioning receptors on the postsynaptic membrane. As both false-negative and false-positive results can be seen with the tensilon test, it is still important to use the blood test for serum antibodies against acetylcholine receptors to confirm the diagnosis of myasthenia gravis.

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