Brainstem Midline Assessed by Transcranial Sonography in Parkinson's Disease: Further Evidence of a Different Etiopathogenesis of Alexithymia and Depression

Objective: Parkinson's disease (PD) is often characterized by altered emotional processing, such as depression and alexithymia. Alexithymic and depressive symptoms may be partially overlapping and the relative independence of these two disorders is strongly debated. Reduced echogenicity of midbrain raphe, evaluated with transcranial sonography (TCS), is a characteristic finding in depression associated with PD. No data are available on brainstem's echogenicity in alexithymic PD patients. We assessed, by means of transcranial sonography, possible differences between PD patient with or without alexithymia and/or depression. Methods: We recruited 22 PD patients among our local cohort of 200 patients referred to our Movement Disorder Center during 2014. All patients were treated with optimal dose of dopaminomimetic (L-DOPA EQ mg 499.7 ± 256.3) and underwent neuropsychological tests including Beck Depression Inventory (BDI) and Toronto Alexithymia Scale-20 (TAS-20). Motor symptoms were assessed with Unified Parkinson's Disease Rating Scale (UPDRS III) and modified Hoehn and Yahr scale (H&Y). TCS was performed, through temporal window, using a color-coded phasedarray ultrasound system (SONOS 7500), to evaluate midbrain raphe (0=absent, 1=discontinuous, 2=continuous). Results: TAS-20 and BDI identified 4 patients with depression without alexithymic symptoms (18.18%), 7 alexithymic patients without depression (31.82%), 5 PD patients with depression and alexithymia (22.73%) and 6 PD patients without any of the two disorders (27.27%). At statistical analysis hypoechogenicity correlated with BDI score and the presence of alexithymia was not significantly correlated with absent or discontinuous raphe. Conclusion: The study evidenced the presence of hypoechogenicity in the midbrain raphe in PD patient with depression. No alteration of midbrain raphe was found in PD patients with alexithymia. These findings suggest that while depression in PD may involve central component of brainstem midline, constituting the basal limbic system, called mesocorticolimbic pathway, alteration in alexithymia does not affect the midbrain. This study provides further evidence that depression and alexithymia are independent affective disorder.