The occurrence of a severe thrombophlebitis limited to one arm during the period of involution of the eruptive stage of pityriasis rosea seems well worth recording, especially since complications and sequelae of pityriasis rosea are practically unknown. Known causes of thrombophlebitis and conditions in which thrombophlebitis is sometimes seen as a complication were not present.
It is astounding how voluminous the literature has become regarding the etiology of a disease as comparatively insignificant as pityriasis rosea. Of the various hypotheses advanced as to the etiology, the theory that pityriasis rosea is a feebly infectious disease probably has the most adherents.
The occurrence of thrombophlebitis as a complication or sequela of pityriasis rosea certainly seems to favor an infectious etiology, the lesions in the walls of the veins being due to injury by an infectious agent or by toxins elaborated by an infectious agent. That thrombophlebitis may occur as a