Acute Cerebellitis-is it infectious or post infectious?

12 yr old boy had febrile episode of 5 days before developing seizures, and ataxia with altered sensorium and shows  on MRI,  an ill defined possibly” C “shaped , subtly enhancing  fluid signal intensity on all pulse sequences , of predominantly white matter regions  of posterior fossa, with more of vasogenic  rather than cytotoxic oedema ,  mass effect on 4^th ventricle, leading to  proximal hydrocephalus  and no bleed- picture suggestive of post infectious BRPINDs (Benign  Regressive  Post   Infectious Neurological  Disorders)

Teaching points by Dr MGK Murthy.  Contributors- Mr Hamid and  Mr Gupta

1.      Infectious edema  can be diagnosed by (a) short duration ,(b) gray matter as site of involvement,(c) decreased mental status  and (d) abnormal CSF, with post infectious exhibiting  opposites of these characteristics

2.      “C” shape is apparently on account of myelinating axons separating the areas of edema

3.      Post infectious demyelinating oedema is possible

4.      BRPINDs  usually exhibit good prognosis with no residual  disabilities

5.      These can be of ADEM variety where brain and cord are involved, or neuromyelitis optica where only optic nerves and cord are involved or only cerebellar variety (as in this case)

6.      MRI  is usually diagnostic  with CSF playing complementary role

7.      BRPINDs could be caused by bacterial/viral/vaccination (MMR)/drugs(arsenic, gold and sulfas etc)/Miscellaneous(herbal extracts etc)