According to the 2017 McDonald Criteria, which imaging finding is required to demonstrate dissemination in space (DIS) for MS diagnosis?

Explanation

## Dissemination in Space (DIS) — 2017 McDonald Criteria **Key Point:** The 2017 McDonald Criteria simplified DIS demonstration by requiring at least **1 T2 lesion in at least 2 of 4 anatomically distinct CNS regions**, rather than the older requirement for 3 lesions in specific locations. ### The Four CNS Regions for DIS | Region | Lesion Type | Notes | |--------|-------------|-------| | **Periventricular** | T2 lesions adjacent to lateral ventricles | Most common in MS | | **Juxtacortical** | T2 lesions touching the cortex or subcortical white matter | Cortical involvement increasingly recognized | | **Infratentorial** | T2 lesions in brainstem or cerebellar white matter | Highly specific for MS | | **Spinal cord** | T2 lesions in cervical or thoracic cord | Indicates CNS involvement | ### Why This Criterion Matters - **Dissemination in space** proves that lesions are scattered across different anatomical locations - This supports a multifocal demyelinating process (characteristic of MS) rather than a single focal lesion - Combined with dissemination in time (DIT), DIS helps establish MS diagnosis without waiting for a second clinical event **High-Yield:** A single T2 lesion in each of 2 different regions satisfies DIS — you do NOT need multiple lesions in each region. This makes DIS easier to demonstrate and accelerates MS diagnosis. **Mnemonic:** **PJIS** = **P**eriventricular, **J**uxtacortical, **I**nfratentorial, **S**pinal cord — the four regions for DIS. **Clinical Pearl:** Gadolinium enhancement (indicating active inflammation) is NOT required for DIS; T2 lesions alone suffice. Enhancement is used to demonstrate dissemination in time (DIT) if a second clinical event has not occurred.