History and Physical
A previously well 4-year-old boy who had a fever and chesty cough for 2 weeks presented to the emergency department with increasing fatigue and inability to walk over 3 days. There was no relevant medical or family history. On examination, the boy was lying in bed and afebrile, with a notable reduction in spontaneous movements, and reduced facial expression but a full range of eye movements. His speech was intact but slow. He could follow commands after a delay, for example taking 4 seconds to fully open his eyes. There was increased tone of all four limbs, with rigidity but no spasticity, and normal tendon reflexes.
Diagnostic Workup
Brain MRI showed symmetric edema in the lentiform nuclei ( Fig. 47.1 ), without diffusion restriction and with other structures spared. MR angiography was normal.
Autoimmune basal ganglia encephalitis. Brain MRI, (A) coronal FLAIR and (B) axial T2 show edema in the bilateral lentiform nuclei. FLAIR , Fluid-attenuated inversion recovery.
Cerebrospinal fluid examination showed mild CSF pleocytosis (22 monocytes per mm 3 ), slightly raised CSF protein (0.44 g/dl), and raised neopterin (137 pmol/L, normal <30), with a normal CSF lactate. Serum showed elevated mycoplasma IgM.
Clinical Differential Diagnoses
For any acute-onset neurologic syndrome, differential diagnoses include acute CNS infection or inflammation (encephalitis, demyelination), acute drug toxicity, biochemical or metabolic derangement, or acute vascular event.
Imaging Differential Diagnoses
Symmetric involvement of the basal ganglia can occasionally be seen with arterial emboli or venous infarcts ( Fig. 47.2 ).
Bilateral embolic strokes in a patient with cardiomyopathy. (A) Head CT, axial, shows bilateral putaminal hypodensities ( arrows ). (B) Head CTA, coronal MIP, shows left MCA cutoff and right MCA short-segment occlusion with distal irregular narrowing ( arrowheads ). MCA , Middle cerebral artery; MIP , maximum intensity projection.
