Monoclonal Gammapathy with the M‐Component Behaving like Donath‐Landsteiner Haemolysin

A case of benign idiopathic monoclonal gammapathy with cold sensitivity due to Donath‐Landsteiner antibody is reported. At the age of 42, the patient noticed a tendency to urticarial wheals after exposure to cold. Two years later, he began to have typical attacks of cold haemoglobinuria. At the age of 46, a haemolysin of the Donath‐Landsteiner type and increased amounts of IgG were disclosed. As the eluted M‐protein gave a positive Donath‐Landsteiner reaction, this was probably identical with the haemolysin. That the gammapathy was of the benign type was supported by the fact that no rise was seen in the M‐protein level or plasma‐cell count at a follow‐up examination 6 1/2 years after the onset of the cold sensitivity. The case is remarkable because Donath‐Landsteiner antibody has not previously been described together with a monoclonal gammapathy. The benign idiopathic monoclonal gammapathy is usually an asymptomatic condition.