For many years hyperplasia of the thymus, either alone or in association with hyperplasia of other lymphoid structures, has been considered as a cause of sudden death in infants and children and as the underlying factor in the production of certain clinical manifestations spoken of as "thymic asthma."
In the literature many theories are found, not only regarding the function of the thymus, but regarding the mechanism by which an enlarged thymus induces dyspnea, cyanosis, stridor, convulsions and death. Whether the symptoms are produced as the result of a specific substance elaborated by the thymus gland, whether they are caused by a gland deficient in specific substances, or whether they are brought about by compression of the trachea, nerves or great vessels remains at the present time unsettled. However, real progress has been made in the recognition of the condition and a satisfactory treatment has been established for its relief.
BLACKFAN KD, LITTLE K. A CLINICAL AND RADIOGRAPHIC STUDY OF THE THYMUS IN INFANTS. Am J Dis Child. 1921;22(5):459-470. doi:10.1001/archpedi.1921.04120050030005