Myeloneuropathy in dogs induced by iodoxyquinoline

Since 1956 many cases of a neurological syndrome characterized by a myeloneuropathy with associated abdominal symptoms and optic atrophy have been encountered in Japan.' Pathologically this syndrome is characterized by systemic degeneration of the long tracts in the spinal cord, especially Goll's column and the corticospinal tract (Fig. l ) , and degeneration of the optic and peripheral nerves.' Therefore, this syndrome has been called subacute myelo-optico-neuropathy (SMON) in Japan. I t has recently been suspected that long-term administration of iodochlorhydroxyquinoline (ICHQ) is a causal factor in this ~ y n d r o m e . ~ . ~ ICHQ was originally manufactured as a dusting powder for skin wounds and as an amebicide, but it is commonly used for the treatment of intestinal bacterial complications in Japan. Some cases of optic atrophy or polyneuropathy or both were reported to be side effects of ICHQ5-7 and o t h e r oxyqu ino l ine derivatives.*-" As for the toxicity of ICHQ, a few animal e x p e r i m e n t s have been reported.' '-' However, SMON, though seen in man, has not yet been reported in animals. We administered ICHQ to dogs orally for a long period and succeeded in eliciting a myeloneuropathy identical clinically as well as pathologically with SMON in man.'4 The results of these animal experiments are reported in this paper.