A SPECT (single photon emission computed tomography using Tc-99m HMPAO) study of brain with segmental quantitative analysis was conducted to access the cerebral perfusion in cases of Down’s syndrome (DS). Varying level of brain hypo-perfusion was documented, probably explaining the neurophysiologic basis of cognitive and neuropsychological deficits, which are not well understood in DS.

Key words: Cognitive deficit, cerebral perfusion, SPECT, Tc-99m HMPAO, neuropsychological deficits.

The neurophysiologic basis for these cognitive deficits (mental retardation, deficit in language and memory etc.) in down syndrome still remains poorly understood. Autopsy on these cases have reported decrease in the spinous processes of apical dendrites of the pyramidal neurons [1], lack of granular cells [2], early appearance of neurofibrillary tangles, senile plaques or both at the age of 30-40 years, and, incomplete or delayed myelination in some cerebrocortical regions viz. frontotemporal lobes and in cerebellocortex, especially in U fibers [2]. In general there is an overall decrease in metabolic need of oxygen to maintain the resting membrane potentials and hence, decrease, in cerebral perfusion [3-5]. Therefore, we conducted SPECT HMPAO study to assess the quantitative segmental cerebral perfusion in cortical and subcortical areas of brain in children with Down Syndrome.

We enrolled 10 patients with Down’s syndrome (proved trisomy 21 on karyotyping) with 5 age matched control with mean age of 6 ± 1.5 years (4.5-8 years). In both groups, only those children were selected, whose EEG and MRI were normal. Informed consent was taken from parents. The study was approved by the Ethical Clearance Committee of Krishna Ram Ayurvigyan Shodh Sansthan (KRASS).

The patients were evaluated by SPECT [6] using Technetium-99m d, l, hexamethylpropyleneamine oxime [99mTc] HMPAO. Analysis was conducted for perfusion studies using segmental quantitative method (Xeleris brain SPECT segmental analysis application).

Review of literature reported lowered cerebral perfusion in fronto-parieto-temoporal region and reduced cortical activity in Down Syndrome [3-5]. A correlation between the degree of cerebral hypoperfusion in DS and retarded developmental was also reported, especially in personal-social and fine motor skills (such as stereotypic movements and echophenomena). The altered perfusion in left medial prefrontal cortex was associated with impairments in communication and social interaction [7,8] and altered perfusion in left anterior cingulate gyrus was associated with impairments in communication, social interaction and obsessive desire for sameness [9]. Sears, et al. [10] reported stereotyped and ritualistic behavior due to subcortical dysfunction, whereas poor functioning of paleocortically derived regions of the thalamus and basal ganglia were associated with defect in response modulation, planning, sequencing and attention.

This study provides a direction to understand the mechanism of cognitive dysfunction, abnormal responses to sensory stimuli, obsessive desire for same-ness, impairment in communication and social interaction observed in children with Down syndrome.