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Middle interhemispheric variant of holoprosencephaly: a distinct cliniconeuroradiologic subtype
A J Lewis1, E M Simon, A J Barkovich
1Stanford University School of Medicine and Lucile Packard Children's Hospital, CA, USA.
Background:
The middle interhemispheric variant (MIH) is a subtype of holoprosencephaly (HPE) in which the posterior frontal and parietal areas lack midline separation, whereas more polar areas of the cerebrum are fully cleaved. While the neuroradiologic features of this subtype have been recently detailed, the clinical features are largely unknown.
Objective:
To present the clinical manifestations of MIH and to compare them with classic subtypes (alobar, semilobar, and lobar) of HPE.
Methods:
The authors evaluated 15 patients with MIH in a multicenter study. Neuroimaging and clinical data were collected and correlated. They compared the data with those of 68 patients who had classic HPE.
Results:
The frequency of endocrinopathy in MIH (0%) was lower compared with the classic subtypes (72%) (p < 0.0001). This correlated with the lack of hypothalamic abnormalities. The percentage of patients with seizures (40%) did not significantly differ from classic HPE. Spasticity was the most common motor abnormality, seen in 86% of MIH patients, similar to other subtypes. The frequency of choreoathetosis in MIH (0%) was lower than that for semilobar HPE (41%) (p < 0.0039). This correlated with the lack of caudate and lentiform nuclei abnormalities. Developmental functions, including mobility, upper-extremity function, and language, of the MIH group were similar to the least severe classic type, lobar HPE.
Conclusion:
MIH is a recognizable variant of HPE with differing clinical prognosis. Similar to the lobar subtype by functional measures, MIH differs from classic HPE by the absence of endocrine dysfunction and choreoathetosis.
Insights
Middle interhemispheric variant (MIH) holoprosencephaly differs from classic forms by lacking endocrine dysfunction and choreoathetosis. MIH patients show similar functional outcomes to the lobar subtype of holoprosencephaly.
Area of Science:
- Neurology
- Developmental Biology
- Genetics
Background:
- Middle interhemispheric variant (MIH) is a subtype of holoprosencephaly (HPE) characterized by incomplete midline separation in posterior brain regions.
- While neuroradiologic features of MIH are known, its clinical manifestations remain largely uncharacterized.
Purpose of the Study:
- To delineate the clinical features of MIH.
- To compare the clinical presentation of MIH with classic HPE subtypes (alobar, semilobar, lobar).
Main Methods:
- A multicenter study involving 15 patients with MIH.
- Correlation of neuroimaging and clinical data.
- Comparison with clinical and imaging data from 68 patients with classic HPE.
Main Results:
- MIH patients exhibited a significantly lower frequency of endocrinopathy (0%) compared to classic HPE subtypes (72%), correlating with absent hypothalamic abnormalities.
- Seizure incidence (40%) and spasticity (86%) in MIH were comparable to classic HPE.
- Choreoathetosis was absent in MIH, contrasting with semilobar HPE (41%), linked to normal basal ganglia development.
- Functional outcomes in MIH, including mobility, upper-extremity function, and language, were similar to lobar HPE.
Conclusions:
- MIH represents a distinct subtype of HPE with a unique clinical profile and prognosis.
- MIH is differentiated from classic HPE by the absence of endocrine dysfunction and choreoathetosis.
- Functional outcomes align MIH with the milder lobar HPE subtype.