Objective: To explore the composition characteristics of traditional Chinese medicine (TCM) syndromes in patients with acute ischemic stroke of yin or yang syndrome by investigating the characteristics of TCM syndromes at different periods after onset.
Methods: One thousand two hundred and forty-six patients with acute ischemic stroke were admitted in twenty hospitals. According to the "diagnostic criteria of syndrome differentiation of stroke", the characteristics of syndromes in the patients were investigated at the periods of 1-3 days, 4-10 days and 11-30 days after they had ischemic stroke. General distribution of six basic syndromes was compared between the patients with yin syndrome and the patients with yang syndrome at the three periods. The six basic syndromes were wind syndrome, pathogenic fire syndrome, phlegm syndrome, blood stasis syndrome, qi deficiency syndrome, and syndrome of yin deficiency and yang hyperactivity.
Results: The percentages of wind, pathogenic fire, and phlegm syndromes in the patients were decreased at the period of 11-30 days as compared with the period of 1-3 days (87.1% vs 79.3%, 52.1% vs 38.7% and 67.1% vs 57.4% respectively, P<0.01). However, the percentages of the syndromes of blood stasis, qi deficiency, and yin deficiency and yang hyperactivity were similar at the three periods (P>0.05). There were no differences in the distribution of yin and yang syndromes among the three periods (P>0.05). The percentages of syndromes of wind, pathogenic fire, phlegm, and yin deficiency and yang hyperactivity were higher (P<0.01), and the percentages of syndromes of blood stasis and qi deficiency were lower (P<0.05, P<0.01) in patients with yang syndrome than in patients with yin syndrome. The complex of three syndromes was the most frequent composition pattern in the patients at the three periods. The percentages of complex syndromes of four or five syndromes were higher, and the percentages of single-syndromes and complex syndromes of two syndromes were lower in patients with yang syndrome than in patients with yin syndrome (P<0.05, P<0.01). The most frequent complex syndromes in patients with yin syndrome were complex syndrome of wind, phlegm, blood stasis and qi deficiency, and complex syndrome of wind, phlegm and qi deficiency; while the most frequent complex syndromes in patients with yang syndrome were complex syndrome of wind, pathogenic fire, phlegm and qi deficiency, and complex syndrome of wind, pathogenic fire and phlegm.
Conclusion: The main discrimination between the yin and yang syndromes is that the yang syndrome is characterized by pathogenic fire. The syndromes of phlegm, qi deficiency, and blood stasis are not associated with the diagnosis of yin or yang syndrome.

Key words: stroke, symptom complex, yin syndrome, yang syndrome, clinical trial, multicentre