AMS (atypical measles syndrome): An altered expression of measles, AMS begins suddenly with high fever, headache, cough, and abdominal pain. The rash may appear 1 to 2 days later, often beginning on the limbs. Swelling (edema) of the hands and feet may occur. Pneumonia is common and may persist for 3 months or more.
AMS occurs in persons who were incompletely immunized against measle. This may happen if a person were given the old killed-virus measles vaccine (which does not provide complete immunity and is no longer available); or the person were given attenuated (weakened) live measles vaccine that was, by accident, inactivated during improper storage. Immunization with inactivated measles virus does not prevent measles virus infection. It can, however, sensitize a person so that the expression of the disease is altered, resulting in AMS.
Being atypical, AMS can be confused with other entities including Rocky Mountain spotted fever, meningococcal infection, various types of pneumonia, appendicitis, juvenile rheumatoid arthritis, etc.