While it is usually stated that the central nervous system (brain and cord), remains uninvolved yet we note axonal degeneration in the cells of the nuclear centres of the affected peripheral nerves as shown by convexity of the cell sides, dislocation of the nucleus and disappearance of the tigroid substance. The striking feature of the pathology of beriberi is the involvement of the vagus nerve and there is evidence of degenerative changes in the cells of the vagal origin in the floor of the fourth ventricle.
Various investigators have shown that in fowls marked peripheral neuritis can exist long before clinical manifestations appear and that typical cases of beriberi may show striking improvement following vitamine administration, notwithstanding the continued existence of peripheral nerve degeneration. For such reasons Vedder thinks the more important changes to probably belong to cells of cord and brain.
McCarrison has noted striking changes in the endocrine glands in avian polyneuritis, particularly hypertrophy of the adrenals and atrophy of the other glands of internal secretion. He attributes the oedema to increase in adrenalin content. Shimbo has reported adrenal hypertrophy in 14 human cases of beriberi.
Symptomatology
It is well to remember that beriberi is but a form of multiple neuritis which in many cases shows only motor and sensory disturbances of the lower portions of the upper and lower extremities.
In fact an extensive epidemic of arsenical neuritis, or, to be more exact, a neuritis in which both alcoholic and arsenical factors were operative, was regarded by eminent authorities as beriberi.
The key to beriberi, however, is the peculiar and striking selection of the vagus nerve in the degenerative processes as well as those of the peripheral nerves of the extremities. It is vagal involvement, giving disturbances of heart particularly and lungs in less degree, which chiefly differentiates beriberi from other forms of multiple neuritis.
Another peculiarity of beriberi is the tendency to vasomotor involvement as shown in the patchy areas of oedema.
Epidemic Dropsy.—Beriberi is typically a nonfebrile disease. There is, however, a disease with fever, called epidemic dropsy, which seems to have a similar etiology to beriberi. It also shows the symptoms of a peripheral neuritis plus cardiac disturbances. In fact Pearse has maintained the identity of the two diseases. Greig considers epidemic dropsy as resembling ship beriberi.
The first record of epidemic dropsy was during a famine in Southern India in 1877. Outbreaks again occurred in 1902 and 1907. The fact that it is a disease which often shows a house infection has caused the advancing of a theory that the bedbug transmits the disease.