Myoclonic Seizure
This is a myoclonic seizure (Answer C), characterized by sudden, brief, shock-like muscle contractions occurring in a conscious patient. 1
Key Diagnostic Features
Myoclonic seizures are defined by sudden, brief, involuntary jerks lasting only a fraction of a second, with preserved consciousness during the event. 1 This distinguishes them fundamentally from the other seizure types presented:
Why Not Tonic (Answer B)?
- Tonic seizures involve sustained, forceful muscle contractions rather than brief jerks 1
- They cause forceful extension of extremities and typically result in loss of consciousness 1
- The sustained nature contradicts the "sudden contraction" described in this case
Why Not Clonic (Answer A)?
- Clonic seizures consist of massive, synchronous, rhythmic jerks involving repetitive rhythmic contractions 1
- They involve many movements (typically 20-100) rather than single brief jerks 2
- Clonic seizures are most commonly associated with loss of consciousness 1, which is absent in this patient
- The movements occur at a frequency of 0.2-5 Hz with synchronized brief tetanic contractions alternating with silent periods 3
Clinical Distinction from Syncope
A critical pitfall is confusing myoclonic seizures with syncope-related myoclonus. 1 The key differences:
- Epileptic myoclonic seizures occur while the patient is conscious or begin at/shortly after onset of any loss of consciousness 1
- Syncopal movements are typically asynchronous, limited in scope, and occur after loss of consciousness and fall 1, 4
- In syncope, there are few movements (not many), and they lack the synchrony and rhythmicity of epileptic seizures 2
Terminology Clarification
The term "myoclonus" describes individual abrupt involuntary movements, while "clonic" is restricted to epilepsy with rhythmic, massive jerks. 1 Myoclonic movements can occur with preserved consciousness, making this the correct answer for a conscious patient experiencing sudden arm contractions. 1