The rare cases of concomitant myasthenia gravis (MG) and Parkinson’s disease (PD) may simply be coincidental, according to a study describing 20 years of experience at a clinical site in Italy and published in the International Journal of Neuroscience.
When comparing MG patients with PD (n=12) and MG patients without PD (n=334), the only variables found to be significantly different between the groups were that the patients with MG were predominantly male and had 3 or more comorbidities. Almost all of the MG patients with PD were male (11/12; 91.6%) compared to around half of the patients without PD (177/334; 52.9%; P <.001). Over half of the MG patients with PD (7/12; 58%) also had 3 or more comorbidities, compared to only 17% (57/334) in the non-PD group (P <.001).
The main comorbidities present in the patients with PD included hypertension and other vascular issues (66.7%) as well as autoimmune comorbidities (33.3%). Other comorbidities included diabetes mellitus and neoplastic disorders.
PD occurred in only 1.9% of the full cohort of MG patients. In the full cohort, MG occurred in all patients at age 50 years or older and was categorized as late-onset. Of the patients with PD, the Myasthenia Gravis Foundation of America (MGFA) clinical status was I (ocular MG) in 50% of patients at diagnosis. The other half of cases were ranked either IIa or IIb.
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The major initial MG symptoms of the patients with PD included ptosis and diplopia in 6, dropped head in 3, and dysarthria, dysphonia, and dysphagia in the remaining patients. The motor symptoms were mostly asymmetric with the nondominant side primarily affected. The majority of patients had stable MG following intervention at the time of last follow-up.
In regards to PD progression, only half of the patients showed a worsening of symptoms through changes in the modified Hoehn and Yahr (mHY) staging. The uneven progression of PD symptoms compared to MG symptoms seen in the study may suggest that the 2 diseases evolve independently.
The authors acknowledged the diagnosis of MG in patients with PD can be challenging due to overlapping symptoms but should be considered since early diagnosis and treatment are essential to both conditions.
“The diagnosis of MG in a patient with PD is challenging. Some commonly reported symptoms, such as hypophonia, dysarthria, [and] dysphagia may be misclassified as referrable to both conditions,” the authors said.
“In addition, blepharospasm induced by anti-PD medications or eye-lid apraxia can be confused with diplopia due to myasthenic external ocular muscle weakness. The motor fluctuations which are [a] hallmark of MG can be embedded in PD due to on/off phenomena,” they added.
Iori E, Mazzoli M, Ariatti A, et al. Myasthenia gravis crossing Parkinson’s disease: a 20 year study from single Italian center. Int J Neurosci. Published online July 15, 2022. doi:10.1080/00207454.2022.2107517