Rare diseases · Sign or symptom
Focal atonic seizure
HP:0020220
What it means
A focal seizure characterized at onset by sudden loss or diminution of muscle tone without apparent preceding myoclonic or tonic activity, typically lasting more than 500 ms but less than 2 seconds. It may involve the head, trunk, jaw or limb musculature.
Rare diseases that can present with this1
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Localised atonic seizure · Localised hypotonic seizure · Localized atonic seizure · Localized hypotonic seizure · Partial atonic seizure · Partial hypotonic seizure · Segmental atonic seizure · Segmental hypotonic seizure
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.