A seasonal periodicity in relapses of multiple sclerosis? A single-center, population-based, preliminary study conducted in Bologna, Italy

Table 1 Chronobiologic analysis of seasonal distribution of multiple sclerosis relapses, and meteorological data

	N	Period (hours)	PR (%)	MESOR ± SE	Amplitude	Acrophase	p
Total relapses	164	8766.00	10.7				N.S.
		4383.00	64.0				0.012
		Overall	74.7	13.69 ± 0.83	6.42	-142° (May)	0.030
Females	108	8766.00	12.1				N.S.
		4383.00	29.6				N.S.
		Overall	41.7	9.01 ± 0.95	3.62	-139°	N.S.
Males	56	8766.00	2.3				N.S.
		4383.00	35.1				N.S.
		Overall	37.4	4.68 ± 0.87	2.81	-144°	N.S.
< 40 yrs	115	8766.00	2.7				N.S.
		4383.00	64.9				0.021
		Overall	67.6	9.60 ± 0.72	4.37	-142° (May)	0.065
≥40 yrs	49	8766.00	41.0				0.031
		4383.00	34.9				0.043
		Overall	75.8	4.09 ± 0.26	2.11	-141° (May)	0.025
Temperature (°C)		8766.00	97.4	15.4 ± 0.39	10.05	-188.8 ± 3. 2 (July)	< 0.001
Humidity (%)		8766.00	81.2	61.0 ± 1.65	14.57	-3.3 ± 9.2 (January)	< 0.001
Wind speed (m/sec)		8766.00	63.1	2.20 ± 0.11	0.63	-164.7 ± 14.6 (June)	0.011
Rain precipitation (mm)		8766.00	0.7	1.81 ± 0.47	0.17	-20.8 ± 227.1	N.S.

Abbreviations (see text for details) derived by Cosinor analysis of the time series data: PR : percentage of rhythm - MESOR: midline estimated statistic of rhythm (the rhythm-adjusted mean over the time period analyzed, i.e., the monthly mean for a cycle of one year) - Amplitude: one-half the difference between the absolute maximum and minimum of the fitted curve - Acrophase: the absolute time of the peak expressed in degrees, with 360° = 12 months or 1 day = 0.9863, as a negative value (i.e., a delay) in reference to midnight December 31. P value derived by the F-test statistic of the null hypothesis that the amplitude of the fitted cosine approximation of a given period = 0⁷

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