Background: Colony stimulating factor 1 receptor (CSF1R) mutations have various clinical, often overlapping, phenotypes. Methods: Case report and literature review. Results: We present a case of a previously independent 49-year-old woman with a 3-year history of early- and insidious-onset, rapidly progressive symptoms resembling CBS (parkinsonism, severe apraxia, global cognitive impairments, personality changes, depression, and functional decline). Brain MRI showed severe atrophy with frontoparietal predilection, asymmetric ex vacuo dilatation, atrophic corpus callosum, and patchy, asymmetric T2/FLAIR hyperintensities in the subcortical white matter. Spine MRI showed no cord signals. Brain MR spectroscopy revealed elevated choline with reduced N-acetyl-aspartate levels. The vasculitis screening, and leukodystrophy and CADASIL workups were all unremarkable. Finally, whole exome sequencing was done and a heterozygous variant of CSF1R (c.1735C>T, p.Arg579Trp) was found. Conclusions: Our patient’s novel CSF1R variant was found to be associated with ALSP. This report supports the utility of a comprehensive genetic testing in adult patients clinically presenting as CBS but with white matter abnormalities on T2-weighted MRI. Given that ALSP has several other clinical and radiologic mimickers, whole exome sequencing proves fundamental and can improve the diagnostic rates and understanding of ALSP. A well-informed diagnosis can lead to appropriate preventive genetic counseling to affected families.