Myasthenia Gravis in Cats: Symptoms, Treatment, and Prognosis
By Dr. Zubair Khalid, DVM, MS, PhD ·
Myasthenia gravis in cats symptoms usually show up as sudden weakness that gets worse with activity, a head that droops or tilts, and trouble eating or breathing. It is a rare autoimmune disease that blocks the signals between nerves and muscles, so the muscles simply cannot respond the way they should. Some cats recover fully with treatment, and some go into remission on their own, but the outlook depends on how severe the disease is and whether a thymoma is involved.
This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- The most common sign is generalized muscle weakness, often without the megaesophagus (a stretched, floppy esophagus) that dogs with the same disease usually have [1].
- Acquired myasthenia gravis is an autoimmune condition, and it is more often linked to a cranial mediastinal mass in cats than in dogs [1].
- Diagnosis is confirmed with an acetylcholine receptor antibody titer, and values above 0.3 nmol/L are considered positive [1].
- Treatment usually involves pyridostigmine, immunosuppressive drugs such as steroids, and sometimes surgery if a thymoma is found [2][3].
- Cats without a cranial mediastinal mass can do very well, with immune remission within 6 months of diagnosis in one case series, including some cats that received no treatment at all [4].
What Is Myasthenia Gravis in Cats?
Myasthenia gravis is a disorder of the neuromuscular junction, the tiny gap where a nerve tells a muscle to move. In the acquired form, the immune system makes antibodies against the acetylcholine receptor, the docking point for the nerve's signal [2]. With those receptors blocked or destroyed, muscles get weak, especially after repeated use.
There are two broad forms in cats. Acquired myasthenia gravis is autoimmune and can appear at any adult age. Congenital myasthenic syndromes are genetic and present early in life, and they are seen more often in Devon Rex and Sphynx cats [3]. The two look similar to an owner but have very different causes and testing.
Acquired disease is uncommon in cats compared with dogs, which is one reason it can be missed early [2][5]. It also behaves a little differently. In cats, generalized weakness without megaesophagus is the usual picture, and a cranial mediastinal mass is more common than it is in dogs [1].
Myasthenia Gravis in Cats Symptoms: What Owners Notice First
The signs come from muscles that cannot sustain effort. They often appear suddenly and can worsen over days.
Weakness and fatigue
Your cat may stumble, sit down after a few steps, or struggle to jump onto a favorite chair. Weakness tends to worsen with activity and improve with rest, which is the hallmark of this disease. In one report, a cat went from hindlimb weakness to full tetraplegia (weakness in all four limbs) within 4 days [2].
Head and neck changes
A droopy head or a head tilt can be an early clue. Positioning head tilt was observed at diagnosis in two cats with myasthenia gravis, and the authors suggest it may relate to muscle spindle dysfunction [6]. If your cat holds its head in an unusual position, that alone is worth a veterinary visit.
Eating, swallowing, and breathing
Regurgitation and trouble swallowing are common in cats with this disease [5]. Food may come back up shortly after eating, or your cat may drool or cough while eating. Respiratory muscle weakness is the most dangerous sign because it can lead to respiratory failure [2]. If your cat is breathing hard, breathing with its belly, or tiring while resting, that is an emergency.
Other findings
Some cats have muscle pain or elevated muscle enzymes. Serum creatine kinase activity was increased in 6 of 8 cats in one case series, and muscle biopsies showed inflammation consistent with polymyositis in several of them [5]. A wobbly gait can have many causes, so a veterinarian needs to sort out which one fits your cat. For a broader look at balance and coordination problems, see Why Is My Cat having a wobbly gait? Cerebellar Hypoplasia and Vestibular Disease.
Causes and Risk Factors
Acquired myasthenia gravis is autoimmune, meaning the body attacks its own acetylcholine receptors [2]. Why that starts is not always clear, but a few triggers and risk factors stand out.
Thymoma and other mediastinal masses
A cranial mediastinal mass is found more often in cats with this disease than in dogs [1]. In one series, 5 of 8 cats had a cranial mediastinal mass, and 3 of those were confirmed thymomas [5]. A thymoma is a tumor of the thymus gland, and removing it can be part of treatment. In one severe case, a cystic thymoma was linked to fulminant disease with rapid progression and a poor prognosis [2].
Breed and genetics
Abyssinian and Somali cats had an increased incidence of acquired myasthenia gravis compared with mixed breed cats in a large case review [1]. Congenital myasthenic syndromes are inherited in an autosomal recessive pattern and are particularly prevalent in Devon Rex and Sphynx cats [3].
Medication reaction
Methimazole, a common treatment for hyperthyroidism, can trigger acquired myasthenia gravis in some cats. In one report, a cat on transdermal methimazole developed generalized weakness and regurgitation, and signs resolved after the drug was stopped and pyridostigmine was started [7]. If your cat is being treated for hyperthyroidism and becomes weak, tell your veterinarian right away. You can read more about that condition in Feline Hyperthyroidism: Signs, Diagnosis, and Treatment.
How Veterinarians Diagnose It
Diagnosis starts with a full physical and neurologic exam, then moves to specific testing.
Blood work and antibody testing
A complete blood count and serum biochemistry are standard first steps [6][2]. The confirmatory test for acquired myasthenia gravis is an acetylcholine receptor antibody titer, measured by immunoprecipitation radioimmunoassay, with values above 0.3 nmol/L considered positive [1]. This is the gold standard for the acquired form [3].
Imaging
Radiography and ultrasonography help look for a cranial mediastinal mass and check for megaesophagus [6][2]. Thoracic imaging is part of the standard workup for any cat suspected of having this disease [4].
Electrodiagnostics and muscle biopsy
Repetitive nerve stimulation can show a decrement in the compound muscle action potential, which supports the diagnosis [5]. Electromyography may reveal positive sharp waves and fibrillation potentials [2]. Muscle biopsies can identify concurrent polymyositis, which was found in several cats with confirmed disease [5].
Ruling out other causes
Because weakness has many causes, your veterinarian will also consider other neuromuscular and metabolic conditions. If the disease is congenital, a genetic mutation must be identified in addition to the clinical signs, since antibody testing is negative in those cats [3].
| Test | What it looks for | Why it matters |
|---|---|---|
| Acetylcholine receptor antibody titer | Autoantibodies against the receptor | Confirms acquired myasthenia gravis above 0.3 nmol/L [1] |
| Chest radiographs and ultrasound | Cranial mediastinal mass, megaesophagus | Guides treatment and surgery decisions [6][2] |
| Repetitive nerve stimulation | Decrement in muscle response | Supports a neuromuscular junction disorder [5] |
| Muscle biopsy | Inflammation, polymyositis | Identifies coexisting muscle disease [5] |
| Genetic testing | Causative mutation | Distinguishes congenital syndrome from acquired disease [3] |
Treatment Options for Myasthenia Gravis in Cats
Treatment has two goals, support the muscles while the immune attack is brought under control, and remove any trigger such as a thymoma or a drug.
Pyridostigmine
Pyridostigmine is a medication that helps nerve signals reach muscle receptors more effectively. It is commonly used in cats with this disease [7][3]. Your veterinarian calculates the dose from your cat's weight and overall health, so never adjust it on your own.
Immunosuppression
Because the disease is autoimmune, steroids and other immunosuppressive drugs are often part of the plan [3]. These reduce the antibody attack over time. Your veterinarian will monitor for side effects and adjust as needed.
Surgery for thymoma
If imaging finds a cranial mediastinal mass, surgical removal may be recommended. In one severe case, the mass was removed through a left intercostal thoracotomy, though the cat needed prolonged breathing support afterward [2]. Surgery carries real risk, so the decision is made case by case with your veterinarian.
Supportive care
Cats with swallowing problems may need soft food, elevated feeding, or a feeding tube. Cats with breathing difficulty may need oxygen and, in severe cases, mechanical ventilation [2]. Hospitalization is sometimes necessary during the worst phase.
Stopping a trigger drug
If methimazole is the suspected cause, your veterinarian may stop it. In one report, signs resolved after the drug was withdrawn and pyridostigmine was started, and hyperthyroidism was later controlled with a different drug without recurrence [7].
Recovery, Outlook, and Life Expectancy
The outlook varies widely, and it depends heavily on whether a mass is present and how fast the disease progresses.
Cats without a mediastinal mass
These cats can do very well. In one case series of 8 cats with acquired myasthenia gravis and no cranial mediastinal mass, all had an excellent long-term outcome and achieved immune remission within 6 months of diagnosis [4]. Four of those cats received no treatment at all and went into spontaneous remission [4]. That is encouraging news for owners facing this diagnosis.
Cats with a mediastinal mass or severe disease
The picture is more serious. A large case review found an overall euthanasia rate of 58% in cats with acquired myasthenia gravis [1]. Fulminant cases with rapid progression have a poor prognosis, especially when respiratory muscles are involved [2]. This is why early recognition and aggressive support matter.
Remission and relapse
Immune remission means the antibody titer drops and signs resolve. It can happen with treatment or on its own [4]. Some cats need long-term medication, and relapses are possible, so regular rechecks and repeat titers are part of long-term management.
Life expectancy
There is no single number that fits every cat. Cats that reach remission can live a normal lifespan, while cats with thymoma-associated or fulminant disease may have a much shorter outlook [2][1]. Your veterinarian can give you a more specific estimate once the full workup is complete.
Prevention
You cannot prevent an autoimmune disease, but you can lower some risks and catch problems early.
- Avoid methimazole if your cat has had a reaction to it, and ask about alternatives for hyperthyroidism [7].
- Keep regular wellness visits so weakness, regurgitation, or a head tilt gets checked early.
- If your cat is a Devon Rex or Sphynx, ask your veterinarian about congenital myasthenic syndromes and genetic testing [3].
- Tell your veterinarian about every medication and supplement your cat takes, since some drugs can trigger immune reactions [7].
- If your cat has a known mediastinal mass, follow the monitoring plan your veterinarian sets.
Limitations and When to Contact a Veterinarian
This article covers general information only. Every cat needs an individual examination, and only your veterinarian can diagnose and treat your cat.
Contact an emergency clinic immediately if your cat is struggling to breathe, breathing with its belly, collapsing, or unable to swallow. Respiratory muscle paralysis can progress quickly and is life threatening [2].
Call your veterinarian the same day if your cat suddenly cannot walk, has a new head tilt or droopy head, regurgitates after eating, or becomes weak after starting a new medication such as methimazole [6][7].
Schedule a routine visit if you notice slowly worsening weakness, exercise intolerance, or changes in appetite or grooming. Early testing makes a real difference in how well these cats do [4].
Frequently Asked Questions
Can myasthenia gravis in cats go away on its own?
Yes, it can. In one case series, 4 of 8 cats with acquired myasthenia gravis and no cranial mediastinal mass went into spontaneous remission without any treatment [4]. All 8 cats in that group reached immune remission within 6 months of diagnosis [4]. Even so, your cat still needs veterinary monitoring during that time.
Is myasthenia gravis painful for cats?
The disease itself is not typically described as painful, but some cats have concurrent muscle inflammation that can cause discomfort. Serum creatine kinase was elevated in most cats in one case series, and muscle biopsies showed inflammatory changes in several [5]. If your cat seems sore or reluctant to move, tell your veterinarian.
Can kittens get myasthenia gravis?
Kittens can develop congenital myasthenic syndromes, which are genetic and present early in life. These are especially common in Devon Rex and Sphynx cats and require genetic testing for a definitive diagnosis [3]. The acquired autoimmune form is more typical in adult cats.
Does hyperthyroidism treatment cause myasthenia gravis in cats?
It can in some cats. Methimazole has been linked to acquired myasthenia gravis as an adverse drug reaction, and one cat's signs resolved after the drug was stopped [7]. If your cat becomes weak or starts regurgitating while on methimazole, contact your veterinarian right away.
How is congenital myasthenia gravis different from the acquired form?
Congenital myasthenic syndromes are inherited genetic disorders, while acquired myasthenia gravis is autoimmune [3]. Antibody testing is positive in the acquired form and negative in the congenital form, so genetic testing is needed to confirm a congenital syndrome [3]. The two also differ in when signs first appear, with congenital cases showing early onset.
Related Articles
- Cat Hypothyroidism: Symptoms, Diagnosis, and Treatment Options
- Cat Allergy Treatment
- Feline Hyperthyroidism: Signs, Diagnosis, and Treatment
- Why Is My Cat having a wobbly gait? Cerebellar Hypoplasia and Vestibular Disease
- Feline Horner Syndrome: Diagnosis and Management
- Cats Ears Twitching And Shaking Head
References
- Risk Factors and Outcomes in Cats with Acquired Myasthenia Gravis (2001-2012). Journal of veterinary internal medicine, 2015.
- Cystic Thymoma-Associated Fulminant Myasthenia Gravis with Rapid Progression in a Cat: Diagnostic and Therapeutic Challenges. Veterinary sciences, 2026.
- Diagnosing myasthenia gravis versus congenital myasthenia gravis in British Shorthair cats: A case study. Journal of biological methods, 2025.
- Long-term outcome of cats with acquired myasthenia gravis without evidence of a cranial mediastinal mass. Journal of veterinary internal medicine, 2020.
- Evaluation of coexisting polymyositis in feline myasthenia gravis: A case series. Neuromuscular disorders : NMD, 2017.
- Positioning head tilt observed in two cats with myasthenia gravis. JFMS open reports, 2024.
- Immune-mediated myasthenia gravis in a methimazole-treated cat. The Journal of small animal practice, 2012.