Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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September 9, 2021
18q Deletion Syndrome
- Background:
- The 18q deletion syndrome (18q- syndrome) is an autosomal deletion disorder of part of the long arm of chromosome 18 that presents with a highly variable phenotype and severity of symptoms.
- Brain MRI frequently reveals findings compatible with varying degrees of hypomyelination, which–together with other clinical and imaging findings–may raise suspicion for this specific syndrome.
- Clinical Presentation:
- Despite the highly variable phenotype, most commonly the presentation includes hypotonia, developmental delay, short stature, hearing loss and external ear anomalies, dysmorphic facial features, and skeletal anomalies.
- Key Diagnostic Features:
- MRI shows features within the differential diagnosis of hypomyelination (although it is currently not established whether this syndrome indeed causes hypomyelination or astrogliosis due to accelerated myelin turnover); most commonly, T1-weighted images are nearly normal, whereas T2-weighted images show persistent, diffuse white matter hyperintensity with correspondent reduced visibility of the gray-white matter interface. There is typically no progression of myelination in subsequent MRI studies. MRS may show increased concentrations of creatine, myoinositol, and choline with a normal NAA.
- In the specific setting of imaging features within the spectrum of hypomyelination, the presence of external auditory stenosis/atresia is highly characteristic of 18q deletion syndrome.
- All together, the clinical presentation, imaging findings, and high-resolution array analysis, revealing a deletion of the long arm of chromosome 18, enable the final diagnosis.
- Differential Diagnoses:
- Pelizaeus-Merzbacher disease: Lack of myelination, highlighted by the low T1 signal typically involving the internal capsule, corona radiata, and optic radiation; T2-weighted images show near-complete absence of expected low signal in the supratentorial region; spectroscopy MRI often shows a reduction in the NAA peak and decreased choline in the affected areas.
- Pelizaeus-Merzbacher–like disease: Imaging findings are essentially identical to those of Pelizaeus-Merzbacher disease.
- Hypomyelination with congenital cataracts: MRI pattern of hypomyelination with the T2 signal more increased in the periventricular white matter (as compared with subcortical and deep white matter)
- Pol III-related leukodystrophy: MRI findings of hypomyelination, along with cerebellar atrophy and T2 hypointensity of the thalami and/or pallidum
- Oculodentodigital dysplasia: Features of hypomyelination associated with T2 hypointensity of the globus pallidus and putamen, as well as cerebellar hypoplasia
- Hypomyelination with atrophy of the basal ganglia and cerebellum: Early MRI (<2 years after onset) shows a moderate-to-severe lack of myelination with a variable degree of putaminal atrophy and moderate cerebellar atrophy. Later studies show a slowly progressive loss of myelin, but more rapidly progressive atrophy of the putamen (which ultimately completely disappears), caudate, corpus callosum, and cerebellum.
- Trichothiodystrophy with photosensitivity (Tay syndrome): Neuroimaging abnormalities are uncommonly reported and include hypomyelination along with cerebral and cerebellar atrophy.
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Treatment:
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Targeting towards the specific signs and symptoms, according to the systemic phenotype of each individual
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May require medical and surgical management therapies
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