Psychiatric disorders in myasthenia gravis

Transtornos psiquiátricos na miastenia gravis

ARTICLE

Psychiatric disorders in myasthenia gravis

Transtornos psiquiátricos na miastenia gravis

Mariana Inés Ybarra^I; Arthur Kummer^II; Elizabeth Regina Comini Frota^III; José Teotônio de Oliveira^III; Rodrigo Santiago Gomez^III; Antonio Lucio Teixeira^I,III

^INeuropsychiatric Branch, Neurology Unit, University Hospital, Federal University of Minas Gerais (UFMG), Belo Horizonte MG, Brazil

^IIMental Health Department, UFMG

^IIINeuromuscular Disorders Clinic, Neurology Unit, University Hospital, UFMG

^{Correspondence}

ABSTRACT

OBJECTIVE: To investigate the prevalence of psychiatric disorders in patients with myasthenia gravis (MG).

METHOD: Forty-one patients with MG answered to a structured psychiatric interview (MINI-Plus).

RESULTS: Eleven (26.1%) patients were diagnosed with a depressive disorder and 19 (46.3%) were diagnosed with an anxiety disorder. Patients with dysthymia were older (p=0.029) and had longer disease duration (p=0.006). Patients with social phobia also had longer disease duration (p=0.039).

CONCLUSION: Psychiatric disorders in MG are common, especially depressive and anxiety disorders.

Key words: myasthenia gravis, neuropsychiatry, mental health, depression.

RESUMO

OBJETIVO: Investigar a prevalência de transtornos psiquiátricos em pacientes com miastenia gravis (MG).

MÉTODO: Quarenta e um pacientes com MG responderam a uma entrevista psiquiátrica estruturada (MINI-Plus).

RESULTADOS: Onze (26,1%) pacientes foram diagnosticados com transtorno depressivo e 19 (46,3%) foram diagnosticados com um transtorno de ansiedade. Pacientes com distimia eram mais velhos (p=0,029) e tinham maior tempo de doença (p=0,006). Os pacientes com fobia social também tiveram maior tempo de doença (p=0,039).

CONCLUSÃO: Transtornos psiquiátricos na MG são bastante comuns, principalmente transtornos depressivos e de ansiedade.

Palavras-chave: miastenia gravis, neuropsiquiaria, saúde mental, depressão.

Myasthenia gravis (MG) is a prototypical autoimmune disease of the skeletal neuromuscular junction. The clinical symptoms of MG are caused by autoantibodies which in most cases attack the postsynaptic nicotinic acetylcholine receptor (AChR) of the muscle endplate^1,2. In other cases, non-AChR components of the postsynaptic endplate, such as the muscle-specific receptor tyrosine kinase (MuSK), might be attacked by autoantibodies¹. Accordingly, the characteristic symptom of MG is a fluctuating muscle weakness that increases with effort.

Besides motor impairment, MG has been somewhat associated with other neurological symptoms since its first descriptions. For instance, old studies reported increased incidence of epilepsy and electrophysiological changes in patients with MG^3,4. Sleep disorders and memory impairment have also been described in MG, as the cholinergic system plays a major role in these functions^5,6. However, the inappropriate methods of these previous studies precluded the establishment of any causal relationship between these findings and disruption of cholinergic neurotransmission². In addition, more recent studies have argued against central nervous system (CNS) compromise in MG⁷. On the other hand, MG is an autoimmune disease and as such can potentially interfere on the brain function determining behavioral changes, such as depressive disorders and suicidal behavior⁸. Moreover, regarding MG as a chronic, debilitating, life-threatening disease with unpredictable progression, a psychological reaction may be expected in patients diagnosed with the disease⁹. Thus, subject with MG may be at increased risk of psychiatric disorders. Unfortunately studies that systematically investigate psychiatric disorders in MG are scarce. This situation is possibly due to the lower prevalence of MG and a comparatively lower interest to study mental features of the disease¹⁰.

In the current study we aimed to investigate the frequency of psychiatric disorders in a Brazilian sample of subjects with MG.

METHOD

This cross-sectional study included 41 consecutive patients with MG attended at the Neuromuscular Disorders Clinic of University Hospital of the Federal University of Minas Gerais (UFMG), Brazil. A nonprobability purposive sampling method was used because of the rarity of the disease. After their appointment with their neurologist, patients were invited to participate in this study. No patient refused to participate. This study was approved by the local ethics committee, and all subjects gave their written informed consent.

Demographic and clinical data were obtained. Diagnosis of MG was confirmed by detection of acetylcholine receptor antibodies in serum and/or electromyographic evidence consistent with the disease. Patients underwent a psychiatric examination comprised of an internationally validated structured psychiatric interview (MINI-Plus)¹¹.

Comparisons of categorical data were performed using Fisher's exact test. The Mann-Whitney U test was employed for continuous variables. All p-values were two-tailed and a significance level of 0.05 was chosen. Statistical analysis was performed using the SPSS v15.0 software (SPSS Inc., Chicago, IL, USA).

RESULTS

Forty-one patients participated in this study. The sample was composed mainly by females in the fourth decade of life (Table 1). Most patients had the generalized form of the disease. The mean (SD) disease duration was 10.3 (8.0) years and the mean (SD) age of disease onset was 27.1 (13.6) years. A significant proportion of patients (43.9%) was retired or receiving social security disability compensation due to MG, and just 29.3% of them were working. Thirty patients (73.2%) were in use of corticoids, 35 (85.4%) were in use of piridostigmine and 10 (24.4%) were in use of azathioprine.

More than a quarter of the patients (26.1%) were suffering from a depressive disorder (Table 2). Three (7.3%) of them had suicidal ideation. Patients with dysthymia were older (p=0.029) and had longer disease duration (p=0.006). The frequency of anxiety disorders was also remarkably high (46.3%). Female gender associated with specific phobia (p=0.010). Patients with social phobia had longer disease duration (p=0.039) and were in use of lower doses of corticoids (p=0.013). No patient was diagnosed with psychosis. Psychiatric disorders did not associate with the type of pharmacotherapy.

DISCUSSION

Our study has shown a high prevalence of psychiatric disorders in MG, especially depressive and anxiety disorders, in comparison to what is expected in the general population. These results are in line with previous studies about psychiatric disorders in MG. For instance, Magni et al. examined 74 patients with MG and observed that 14% fit DSM-III criteria for an affective disorder and 22% had adjustment disorder with depressed mood and mixed emotional features¹². However, the frequency of anxiety disorders in the study by Magni et al. was remarkably low. By contrast, Paradis et al. reported increased rates of panic disorder (7%) in MG¹³. These authors speculate whether fluctuating respiratory symptoms of MG predispose vulnerable individuals to develop panic disorder and/or agoraphobia. Although anxiety and depressive disorders are probably more frequent in MG patients with respiratory failure, these psychiatric disorders are also prevalent in patients without any respiratory complaint¹⁴. Higher levels of anxiety and tension were also observed by other authors^15,16. Unfortunately, we were not able to evaluate whether anxiety was more frequent in patients with respiratory problems. Bulbar impairment could also explain social anxiety symptoms due to dysphonia, dysarthria and dysphagia.

Sitek et al. showed that MG patients scored higher in the Beck Depression Inventory than healthy controls⁷. Conversely Paul et al. observed that somatic symptoms of depression might be misleading in patients with MG, suggesting that the frequency of depression in MG may be similar to the one found in healthy population¹⁷. It seems that psychiatric disorders in MG are truly more prevalent than in general population, although their frequency probably does not exceed the prevalence of psychiatric disorders in other chronic illnesses^2,18. Hence, psychopathology in MG is possibly due to a psychological reaction to a chronic and unpredictable disease rather than a result of CNS involvement.

Data concerning predictors of psychopathology in MG are still scarce. We observed that longer disease duration was associated with dysthymia and social phobia. Other studies suggested that psychopathology was more prevalent in females and correlated with disease severity^12,19. Paradis et al. found no association between the severity of the disease and anxiety disorders¹³. Also, psychopathology has not been associated with steroid therapy, thymectomy, or age of MG onset¹². Nevertheless, corticosteroids have been associated with depression in several clinical populations²⁰. Indeed, it is known that corticosteroids can alter the levels of monoamines and induce behavioral change, but the use of corticoids was not associated only with depression in this study²¹.

Our study has some limitations. First, patients were recruited in a tertiary center where more complex and severe patients are usually attended. Thus, our results may not be representative of MG patients in general. Second, a type II error of our study cannot be ruled out due to the relatively small sample size enrolled in the study. However, it must be taken into account that MG is an uncommon disease and this study included one of the largest cohort of MG patients of the neuropsychiatric literature. The lack of a control group composed of healthy individuals or patients with other chronic disease is another limitation. Last but not least, considering that current literature has mixed results regarding the association between disease severity and psychopathology^12,13,19, it would be of utmost importance a detailed quantitative assessment of the severity of the disease and a more comprehensive classification of the patients based on the Myasthenia Gravis Foundation of America Clinical Classification²². We hope that future studies will overcome these limitations.

In conclusion, psychiatric disorders in MG are frequent, particularly depressive and anxiety disorders. It is already known that these disorders impact in quality of life of subjects with MG²³. Clinicians should investigate these disorders in order to reduce disease burden.

Received 3 June 2010

Received in final form 20 October 2010

Accepted 27 October 2010

Support: This study was partly funded by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil) and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG, Brazil)

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Publication Dates

• Publication in this collection
  26 Apr 2011
• Date of issue
  Apr 2011

History

• Reviewed
  20 Oct 2010
• Received
  03 June 2010
• Accepted
  27 Oct 2010