Atonic seizure 2010-07-10T03:13:06Z Drop seizures Astatic seizures Astatic seizure Atonic seizures This term describes the initial semiology of the seizure without specifying whether the onset is focal or generalized. Thus it can be used for coding atonic seizures when the onset is not known. UMLS:C0270846 Hypotonic seizures SNOMEDCT_US:42365007 UMLS:C1836509 Drop attacks HP:0002124 Atonic seizure is a type of motor seizure characterized by a sudden loss or diminution of muscle tone without apparent preceding myoclonic or tonic event lasting about 1 to 2 seconds, involving head, trunk, jaw, or limb musculature. Sudden loss of muscle tone HP:0010819 SNOMEDCT_US:189198006 Hypotonic seizure Motor seizure