Mumps encephalitis is not uncommon and is generally considered a mild disease. Death is rare, and recovery is usually rapid and complete.1
However, two facts disturb present complacency with regard to the prognosis of mumps encephalitis. First, there have been reports2 of severe neurologic sequelae: viz., involvement of the third, sixth and seventh cranial nerves, polyneuritis, optic atrophy, deafness, ascending myelitis, hemianopsia, hemianesthesia, complete deviation of the eyes, chorea, myoclonus, ataxia and personality changes. Second, since it is an accepted fact that mumps encephalitis may occur without apparent infection of the salivary glands, instances of masked mumps encephalitis with severe neurologic sequelae may go undiagnosed under the general classification of encephalitis.
In the absence of painful enlargement of the salivary glands or of inflammation of the gonads, the diagnosis of masked mumps encephalitis becomes a problem. When obtainable, a history of contact is valuable. However, results of laboratory procedures,