Repetitive transcranial magnetic stimulation in patients with late life depression influences phenylalanine metabolism

Abstract Repetitive transcranial magnetic stimulation (rTMS) is used to treat different neuropsychiatric conditions like Parkinson’s disease, essential tremor, stroke, cognitive decline, dementia and depression. rTMS may exert its therapeutic effects by influencing the biochemistry of neurotransmitters. In this exploratory study, safety symptom improvement and changes in the availability of neurotransmitter precursor amino acids were studied following prefrontal cortex (PFC) stimulation using repetitive transcranial stimulation with TheraCell apparatus R (Guth Meditec, Salach, Germany) as an additional treatment in ten patients with late life depression. Treatment was well tolerated with no serious adverse effects being observed. rTMS induced a significant improvement in the symptoms of depression and a significant decrease in the HAMD-7 (p <0.03). At the same time, the serum phenylalanine to tyrosine ratio declined significantly (p <0.04). No significant influence of rTMS on tryptophan breakdown and serum neopterin concentrations was observed. These preliminary findings indicate that rTMS may influence the activity of the enzyme phenylalanine hydroxylase (PAH) which plays a key role in the biosynthesis of neurotransmitter precursors related to neuropsychiatric symptoms in late life depression. However, results were obtained from only 10 patients. Larger studies are therefore required to support these conclusions