Table 3. The Number of Predisposing Factors of All of The 24 Patients Provided with Detailed Information

Predisposing factor		Frequency
URI*		10
Stress of Fatigue		7
Exercise		2
Seasonal	Aggravated in spring & summer	1
Idiopathic		1
Not mentioned		11

URI: Upper Respiratory Infection.
In regards to the patients not counted in the table above, a case report¹³⁾ with 106 patients reported that seasonal factor and URI were the most common as predisposing factors. Among the seasonal factor, spring was the most frequent predisposing factor for 50% of patients, followed by autumn with 23.6% of patients. URI was reported among 48.1% of patients as predisposing factor. A literature review¹⁸⁾ of Chinese clinical studies didn’t present with predisposing factors.