Transcranial Magnetic Stimulation in the Treatment of Dual Disorders: Study in Patients with Depression and Tobacco Addiction

Currently, resistant major depression and substance abuse disorder are two highly prevalent mental health pathologies. In the case of depression, the WHO estimates that 3.8% of the world's population suffers from this disorder, which is the result of a complex interaction between social, biological and psychological factors. Multiple sociodemographic factors are related, such as low socioeconomic status, which results in a poorer physical condition that predisposes to depression. In addition, there is also a strong association with different mental illnesses, when associated with an addiction it is called Dual Disorder, with tobacco or alcohol consumption being more frequent. Other factors to highlight are a history of trauma in childhood, being in a situation of divorce/separation, but there is especially a strong association with the female gender. Although the prevalence in the female gender is much higher, no difference is observed with respect to men in terms of the course of the disease and the risk of relapse. The higher incidence of depression in women can be attributed to different factors: biological reasons (hormones and genetic load), psychological reasons (neuroticism, lack of positive affect, rumination or personal dissatisfaction), without forgetting environmental factors: such as sexual abuse or violence in childhood, as well as social inequalities between men and women. This clear difference between women and men justifies and demands the incorporation of a gender perspective in the research, management and treatment of patients diagnosed with major depression. The importance of major depression also lies in the fact that it is the fourth cause of death in the age group between 15 and 29 years and is a common cause of temporary disability due to common contingencies in people of working age, with durations of around 6 months, much longer than the duration estimated by the National Institute of Social Security of 30-60 days. This is reflected in the economic costs, which are estimated to result in an annual public expenditure of up to 10,763 million euros. It is a complex disease that is expected to see its incidence increase in the coming years, which is why it requires a scientific effort for its diagnosis and treatment, especially in resistant cases, because they evolve into a chronic mental illness with higher personal, social and health costs. Nicotine use disorder is also a public health problem, with 50,000 deaths currently attributed to it. The prevalence of 1 in 4 individuals makes it the most common mental illness. Although there has been a decline in consumption among men in recent years, this is not reflected in the same way among women. There are many factors that determine vulnerability to nicotine use disorder, both genetic and psychosocial, highlighting that the early onset of consumption predisposes to a higher risk of addiction, given the brain immaturity in certain brain circuits. Due to biopsychosocial factors common to other mental disorders, it is common for patients with tobacco addiction to present dual disorder, especially depressive disorders. An example is the CHRNA5 gene, encoding the alpha 5 subunit of the acetylcholine receptor, related to nicotine dependence, but also to an increased risk of suffering from mental disorders and, therefore, dual disorders.

It is therefore not an isolated or coincidental fact that both diagnosis coexist in the same individual, an affective disorder such as major depression with addiction to a substance, such as tobacco, which is called dual disorder.

In this group of patients, there is a fact worth mentioning, and that is that both diseases present an increased risk of suicidal ideation. In the case of depression, this relationship has been clearly studied, but an increased risk has also been observed in patients who are smokers or who have been smokers, which is why it is an item that has been included in different clinical scales that assess this ideation. This symptomatology requires special attention for diagnosis and treatment due to its potential lethality.

The need for new lines of treatment arises because in depression, up to 30% of patients are resistant to pharmacological therapies. Although electroconvulsive therapy is currently considered the treatment of choice for resistant depression, it has important limitations, for example due to the need to anesthetize the patient, as well as the frequent side effects that it has on cognitive functions, specifically memory loss, which make it a technique with little social acceptance. Something similar occurs with regard to nicotine use disorder. With the use of drugs such as varenicline (recently withdrawn from the market) or cytisine, the drug of choice currently for the treatment of this disorder, it is observed that only 32% of patients remain abstinent two weeks after having finished the treatment, along with the side effects that make adherence to the treatment difficult.

As a result of the therapeutic limitations described above, neuromodulation techniques, such as the one proposed in the present study: transcranial magnetic stimulation, have gained prominence in recent years.