Approximately 3% of inflammatory demyelinating polyneuropathy cases progress for longer than 4 weeks, the arbitrary cut-off point for the diagnosis of GBS, or they relapse and fluctuate. Such cases are referred to as chronic inflammatory demyelinating polyneuropathy (CIDP). In CIDP, the nadir of illness is usually reached after several months, either after a chronic monophasic, a stepwise progressing, or a relapsing course. In contrast, the even rarer recurrent GBS, in which acute relapses appear after complete recovery, is usually considered to be more closely tied to GBS than to CIDP by most authorities, since time course and treatment response of single recurrences are identical to typical monophasic GBS.