A severe drop in antibodies points to a rare syndrome

Fred, 76, a retired railway worker, has led a very active life. He is a non-smoker and non-drinker who lives with his wife.
As a young man he worked as a plumber’s mate and was exposed to blue asbestos.
In recent weeks he has felt unwell, with loss of appetite. He is not feverish and there is no cough or dyspnoea. He has had several episodes of semi-fluid stools without associated bleeding or mucous.
He denies rash or joint pain. There is no specific weakness or urinary symptoms. Fred has not travelled outside the state in the past five years and has no recent sick contacts.