Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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January 16, 2020
SMART Syndrome
- Background:
- SMART syndrome is a rare and delayed complication of brain radiotherapy and presents with characteristic clinical and brain imaging findings.
- Review of documented reports reveals a greater prevalence among men, with more than twice as many cases being reported than in women. SMART syndrome can affect patients of a wide age range, with there being reports of SMART in adults as old as 69 and children as young as 8.
- Proposed mechanisms for the syndrome include electrographic seizure activity, abnormal autoregulation due to endothelial cell injury caused by radiation-induced vascular dysfunction, and neuronal dysfunction caused by a reduction in the threshold to cortical spreading depression.
- Clinical Presentation:
- Patients suffer recurrent attacks of complex neurologic signs and symptoms 1 to 35 years (mean: 7 years) after brain radiotherapy.
- Signs and symptoms include headache with migrainous features and strokelike focal neurologic deficits (eg, homonymous hemianopsia, hemiplegia, and aphasia).
- Seizures may coexist.
- Key Diagnostic Features:
- Brain MRI shows unilateral localized gyral swelling (involving the previously irradiated parenchyma) with cortico-pial gadolinium enhancement, as well as increased T2/FLAIR signal with or without restricted diffusion, not respecting vascular borders.
- Stigmata of previous radiotherapy are frequent, namely multiple cavernomas or telangiectasias.
- Brain MRI abnormalities tend to be transient and usually subside within weeks to months.
- CSF analysis rules out other etiologies.
- Differential Diagnoses:
- Postictal changes: may be indistingishable, although stigmata of prior radiotherapy should not be present
- Stroke: cortical/subcortical increased T2/FLAIR signal with associated restricted diffusion respecting vascular borders
- Tumor recurrence: new contrast-enhancing nodule or mass usually next to primary tumor localization growing over time and showing mass effect and vasogenic edema
- Radiation necrosis: late-delayed radiation necrosis can have a similar appearance to tumor recurrence; perfusion imaging and spectroscopy may be useful in distinguishing these 2 entities as well with stabilization/reduction in size over time
- Meningitis or leptomeningeal carcinomatosis: both conditions also present with leptomeningeal enhancement and absence of the normal FLAIR supression of the cortical sulci/basal cisterns; lumbar puncture with CSF analysis allows their definitive exclusion
- Treatment:
- Symptoms are usually self-limiting and gradually resolve within 14–35 days.
- Some patients respond rapidly to steroid pulse therapy.
- Antiepileptic agent use may be prudent.
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