A 58-year-old woman with a 15-year history of hypertension and type 2 diabetes mellitus presents with progressive gait disturbance and mild cognitive decline. MRI brain T2-weighted imaging reveals multiple hyperintense lesions in the white matter marked **A** (centrum semiovale), with periventricular caps and halos extending into the subcortical regions. CSF analysis is normal, and oligoclonal bands are absent. Which of the following is the most likely diagnosis?

Explanation

## Why Small vessel ischemic disease (SVID) with vascular cognitive impairment is right The clinical presentation—age >55, long-standing hypertension and diabetes, progressive gait and cognitive decline—combined with the MRI pattern of T2-hyperintense white matter lesions in the centrum semiovale with periventricular caps and halos is pathognomonic for small vessel ischemic disease. According to Harrison 21e Ch 444, small vessel ischemic disease is the most common cause of T2-hyperintense white matter lesions in elderly patients, with risk factors including hypertension, diabetes, smoking, and age. The periventricular and subcortical patchy distribution, absence of CSF oligoclonal bands, and lack of clinical dissemination in space and time exclude multiple sclerosis. The normal CSF and absence of longitudinally extensive spinal cord lesions exclude NMOSD and PML. ## Why each distractor is wrong - **Multiple sclerosis with secondary progressive course**: While MS can present with white matter hyperintensities, the diagnosis requires dissemination in space and time on MRI, positive CSF oligoclonal bands, and/or clinical episodes. This patient's normal CSF, absence of periventricular Dawson fingers, and lack of juxtacortical or infratentorial lesions make MS unlikely. The clinical picture of vascular risk factors and progressive decline without relapses is inconsistent with MS. - **Neuromyelitis optica spectrum disorder (NMOSD)**: NMOSD typically presents with longitudinally extensive (≥3 vertebral segments) spinal cord lesions, area postrema involvement, and optic neuritis. The patient's presentation lacks these hallmark features, and AQP4 antibody testing would be expected to be positive. The periventricular and subcortical pattern is not characteristic of NMOSD. - **Progressive multifocal leukoencephalopathy (PML)**: PML occurs in severely immunocompromised patients (HIV with CD4 <50, or on potent immunosuppressants) and typically presents with asymmetric subcortical white matter lesions. This patient has no mention of immunosuppression, and the symmetric periventricular and subcortical pattern with vascular risk factors is inconsistent with PML. **High-Yield:** Small vessel ischemic disease is the most common cause of T2-hyperintense white matter lesions in patients >55 years with vascular risk factors; periventricular caps and halos are classic. Always exclude MS (oligoclonal bands, dissemination in space/time) and NMOSD (spinal cord lesions, AQP4 antibodies) before diagnosing SVID. [cite: Harrison 21e Ch 444; McDonald 2017 MS criteria]