The subcutaneous thickening evident on MRI indicated P. acromelalga poisoning-induced erythromelalgia involved subcutaneous inflammatory edema. The typical duration of edema without treatment is more than a month. The improvement on MRI after nicotinic acid treatment indicated that the adequate vasodilation induced by nicotinic acid contributed to resolution of the symptoms. Nicotinic acid was associated with the improvement of the edematous changes caused by the P. acromelalga intoxication.