Axonal degeneration in diphtheritic neuropathy

The purpose of this investigation was to study axonal degeneration in a neuropathy known usually to be demyelinating in type. High doses of diphtheria toxin were injected intraneurally into the sciatic nerves of 33 rabbits. At two dose levels the effects were studied histologically at various times after injection. At the higher dose level there were vascular changes from the first day after injection, accompanied between the first and the fifth day by extensive haemorrhages. Schwann cell damage and axonal degeneration which were present from the first and the third day after injection respectively, might therefore be due partly to ischaemia. A slightly lower dose produced almost no endoneurial haemorrhage. At this dose level marked axonal degeneration was present from the twelfth day onward. Reasons are given for the view that this was due to a direct effect of the toxin on the axons. The results of this investigation give further support to the view that axonal degeneration may occur in many demyelinating neuropathies if the underlying process is sufficiently severe.