Alexander disease (Adult type)
General description
Alexander disease is a rare neurodegenerative disorder caused by mutations in the glial fibrillary acidic protein (GFAP) gene, leading to the formation of Rosenthal fibers composed of GFAP, αB-crystallin, and heat shock proteins in astrocytes. The disease is classified into three clinical types: infantile, juvenile, and adult, based on the age of onset and clinical progression.
In adult type Alexander disease, symptoms vary widely and can include spastic paraplegia, bulbar or pseudobulbar palsy, palatal myoclonus, cerebellar ataxia, and dementia. Unlike the infantile type, macrocephaly is not typically seen in adult cases.
References
- van der Knaap, Marjo S., et al. "Alexander disease: diagnosis with MR imaging." American Journal of Neuroradiology 22.3 (2001): 541-552.
Tadpole appearance
In adult-onset Alexander disease, there is no abnormality in the cerebral white matter, but significant atrophy and T2WI/FLAIR hyperintensity of the medulla and cervical spinal cord is present, while the pons remains preserved, creating a characteristic 'tadpole appearance.'
Brainstem pia mater hyperintensity
FLAIR shows hyperintensity in the pia mater of the medulla, occasionally extending to the pons and midbrain.
T2WI and FLAIR hyperintensity
T2WI and FLAIR occasionally show hyperintensity in the middle cerebellar peduncles and dentate nuclei.