Seizure Characterization and Diagnosis

Introduction to Tonic Seizures

A seizure characterized by muscle rigidity without shaking is most likely a tonic seizure, which involves sustained muscle contraction without the rhythmic jerking movements seen in clonic or tonic-clonic seizures, as noted by the European Heart Journal 1
Tonic seizures are distinguished by forceful extension of extremities without rhythmic jerking, stiffening posture that may cause the patient to "keel over like a falling log", according to the European Heart Journal 1
Tonic seizures may cause loss of consciousness, though not always, as reported by the Journal of the American College of Radiology 2
Tonic seizures involve only the rigid phase without the subsequent rhythmic jerking (clonic) movements, as stated by the Journal of the American College of Radiology 2

Tonic-clonic seizures begin with rigidity but progress to rhythmic jerking movements, as described by the European Heart Journal 1
Atonic seizures involve sudden loss of muscle tone (flaccidity) rather than increased tone, as noted by Genetics in Medicine 3
Atonic seizures are rare and typically occur in children with pre-existing neurological problems, according to Genetics in Medicine 4

Tonic seizures may indicate possible structural brain abnormalities in some cases, as reported by Genetics in Medicine 4
Tonic seizures may be triggered by metabolic factors such as hypocalcemia, especially in patients with conditions like 22q11.2 deletion syndrome, as noted by Genetics in Medicine 3 and 4

When evaluating a patient with suspected tonic seizures, obtain detailed eyewitness accounts of the event, focusing on presence of rigidity without rhythmic jerking, duration of unconsciousness, and whether movements began before or after loss of consciousness, as recommended by the European Heart Journal 5
Consider EEG monitoring to capture the event and confirm the diagnosis, as suggested by the European Heart Journal 6
Evaluate for potential triggers such as hypocalcemia or hypomagnesemia, structural brain abnormalities, and medication effects, as reported by Genetics in Medicine 4 and the Journal of the American College of Radiology 2

Tonic seizures may be misdiagnosed as syncope with posturing, as noted by the European Heart Journal 1 and 6
Brief tonic seizures might be confused with cataplexy (sudden loss of muscle tone triggered by emotions), as reported by the European Heart Journal 6
Movements during syncope are typically asynchronous and limited, occurring after the person has fallen, while tonic posturing in epilepsy may occur before the fall, as described by the European Heart Journal 1