Striatal lesions in delusional parasitosis revealed by magnetic resonance imaging

Delusional parasitosis (DP) is a syndrome characterized by the firm conviction that small living beings infest the skin. The etiology can be primary and secondary. Structural brain abnormalities in DP have only been reported in case reports often subcortical vascular encephalopathy and right-hemisphere strokes in the temporo-parietal cortex. Systematic brain imaging studies are lacking. We aimed to identify a brain region with structural lesions in patients with DP in order to better understand the pathophysiology of DP.

Nine consecutive patients with DP in a psychiatric outpatient department were assessed clinically and by means of cranial magnetic resonance imaging (MRI).

Five of the nine cases were diagnosed as having DP as psychotic disorders due to a general medical condition while three had DP arising from pre-existing psychiatric illness and one suffered from a delusional disorder, somatic type (primary form). Four of the five DP cases secondary to a general medical condition (one case could not be analyzed) had striatal lesions predominantly in the putamen. Thalamic or cortical lesions were found in one case, respectively. In the primary DP case and all cases secondary to another psychiatric disorder basal ganglia and subcortical gray matter lesions were absent. In all medical (secondary) DP cases subcortical white matter lesions were found mainly in the centrum semiovale. Three of the five medical DP cases showed severe generalized brain atrophy which was absent in the primary DP case and in the cases secondary to other psychiatric disorders.

We present the findings of the first structural MRI study in DP. Our results suggest a possible relevance of structural lesions in the striatum, predominantly the putamen, in the medical (secondary) DP-subgroup. Our findings are in line with other studies demonstrating that the putamen, in addition to its role in motor regulation, represents a brain area that mediates visuo-tactile perception. Disturbed functioning of the putamen and associated brain areas of the somatic/dorsal striato-thalamo-cortical loop might therefore play an important role in the pathophysiology of DP, which is characterized by somatic delusions, tactile misperceptions and sometimes also visual hallucinations. The involvement of the striatum and the efficacy of antidopaminergic antipsychotics indicate dopaminergic dysfunction in DP. Evidence from DP in intoxication with substances influencing the dopamine transporter (DAT) (e.g. cocaine, methylphenidate, bupropion) further supports this observation. Further neuroimaging studies in larger samples are needed to expand our preliminary knowledge obtained from this case-series study.