Myasthenia Gravis Learning Zone
Transcript: A case of MG post thymectomy
Professor Amelia Evoli
Interview recorded Apr 2024. All transcripts are created from interview footage and directly reflect the content of the interview at the time. The content is that of the speaker and is not adjusted by Medthority.
Good morning to everyone. I'm Amelia Evoli. I'm a neurologist at the neuroscience department of the Catholic University in Rome, Italy. And today, I will discuss with you relapsing myasthenia gravis in a patient with thymoma. This patient's history start with the discovery of thymoma. This was a 53-year-old otherwise healthy man, who was diagnosed with a mediastinal mass during a routine medical check. And radiological findings were consistent with the thymoma. So the patient underwent thymectomy. The thymoma was quite big, but only had minimal extra-intracapsular infiltration and histological examination showed an AB thymoma. AB thymoma is a mixed thymoma, composed of cortical cells and medullary cells. B is the cortical and A, the medullary component. This is a quite benign thymoma that actually is not very often associated with myasthenia gravis. And if we look at the thymoma subtypes in myasthenia gravis patients, these are data from our department, we can see that most commonly, myasthenia gravis associated thymoma subtypes are of B type, particularly the B2 type. But AB thymoma can occur in some patients with myasthenia gravis. So after thymectomy, the patient underwent a radiotherapy. And at that time, there were no signs of myasthenia gravis or other diseases that can occur in association with thymoma. Myasthenia gravis, is by far the most common disease associated with thymoma. But here, you can see a very long list of autoimmune disease that can occur in these patients.
Some of these disease are quite severe. And in our experience, glomerulonephritis, was the most common non-neurological disease in these patients. While neuromyotonia after myasthenia gravis, was the most common neurological disorders. And if we look at the onset of these diseases in relation to thymoma diagnosis and treatment, we can see that the myasthenia gravis, is nearly always diagnosis concurrently with the thymoma as the onset of myasthenia gravis prompts radiological study of the mediastinum and thymoma is diagnosed at this stage if it's there. But if you look at other autoimmune diseases, you can see that they can occur actually at any time and quite often even years after thymoma diagnosis and treatment. Coming back to the story of this patient, a few months after thymectomy and radiotherapy, the patient presented with unilateral fluctuating ptosis. And after a few days, he complained of intermittent diplopia.
So myasthenia gravis was suspected and the diagnosis was confirmed by detection of anti-acetylcholine-receptor antibodies, quite a high-titer, a clear response to oral pyridostigmine while repetitive nerve stimulation in extracranial muscles failed to show a CMAP decrement. Because the patients had disease confined to extrinsic ocular muscle. So we confirmed the diagnosis of anti-acetylcholine receptor-positive ocular myasthenia gravis. And treatment with pyridostigmine 60 mg, three time per day and prednisone 25 mg daily lead to a very quick and significant improvement. However, the subsequent course of the disease wasn't so smooth. You can see here the QMG score, quantitative score to quantify weakness in the disease with maximum score at 39 and the MG-ADL score with a maximum score of 24. At the onset of the disease, the patients had quite low score. Because he had ocular myasthenia gravis.
Prednisone was very effective. He remained in good control of his disease, actually in pharmacological remission and could gradually reduce prednisone. But when he achieved a very low-maintenance dose, 5 mg every other day, he suffered from a disease relapses, still confined to extrinsic ocular muscles. So prednisone was resumed at 30 mg per day. The patient improved, could reduce prednisone. But again, when he reached very low-maintenance dose, suffered from a very severe MG relapses with weakness generalisation. At that time, the patient had severe weakness of lymph muscles and also bulbar symptoms with dysarthria and dysphagia together with the ocular complaints. So he was treated with high-dose prednisone, IVIg and with added azathioprine, a steroid-sparing agent. Unfortunately, azathioprine caused liver toxicity and was withdrawn. But prednisone in monotherapy was sufficient to improve symptoms. Patient achieved with control of his disease, but again, this time, the maintenance dose of 20 mg every other day suffered from a very severe disease relapses. Again, high-dose prednisone, he was treated with plasma exchange and received mycophenolate mofetil as steroid-sparing agent.
However, in the following disease course, mycophenolate wasn't very effective in controlling the disease in reduced steroid dosages. And the patient improved with prednisone but continued to suffer from disease relapses in 2023 and then in January, 2024. And at this point, we decided to start efgartigimod. And efgartigimod administration resulted in very good control of the patient disease and can restore normal life condition in this case. Looking at the patient history after 12 years of steroid treatment, his comorbidities actually were not so severe. He had arterial hypertension. However, the patient is older than 60. At this age, arterial hypertension is not so rare and in any case was well-controlled by therapy. He underwent coronary stenting in 2020 and suffered from herpes zoster infection in 2021. He had no severe osteoporosis or diabetes, but we felt that continuing with high-dose prednisone, these comorbidities could be reasonably expected. And he had no thymoma recurrence. This patient undoubtedly responded very well to prednisone, however, with MG relapses on treatment tapering. This is a very common situation in myasthenia gravis. And very importantly, the minimum effective dose of prednisone increased over time. Azathioprine at the standard dosage induced liver toxicity.
This is not common, but can happen during azathioprine treatment. On the other end, mycophenolate mofetil was very well-tolerated, but was not effective as steroid-sparing agent. Efgartigimod reduce disease severity, restored normal life condition. At that moment, the patient lives a perfectly normal life. And in patients with thymoma, surveillance for hypogammaglobulinemia that is a very rare but potentially a very severe disease associated with thymoma is very important. Because we have seen that this disorder can occur even many years after thymoma treatment. And the surveillance of this possible complication is very important in all thymoma patients treated with blockers of the neonatal Fc receptor. Thank you for your attention.
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