Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL): A challenging diagnosis and a rare multiple sclerosis mimic.

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) is an extremely rare hereditary cerebral small vessel disease caused by homozygous or compound heterozygous mutations in the gene coding for high-temperature requirement A serine peptidase 1 (HtrA1). Given the rare nature of the disease, delays in diagnosis and misdiagnosis are not uncommon. In this article, we reported the first case of CARASIL from Saudi Arabia with a novel homozygous variant c.1156C>T in exon 7 of the HTRA1 gene. The patient was initially misdiagnosed with primary progressive multiple sclerosis and treated with rituximab. CARASIL should be considered in the differential diagnosis of patients with suspected atypical progressive multiple sclerosis who have additional signs such as premature scalp alopecia and low back pain with diffuse white matter lesions in brain MRI. Genetic testing is important to confirm the diagnosis.