What type of seizure is characterized by muscle rigidity without shaking?

Tonic Seizures: Seizures Characterized by Muscle Rigidity Without Shaking

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. 1

Clinical Characteristics of Tonic Seizures

Tonic seizures are distinguished by the following features:

• Sustained muscle contraction/rigidity lasting from a few seconds to minutes 2
• Forceful extension of extremities without rhythmic jerking 1
• Stiffening posture that may cause the patient to "keel over like a falling log" 1
• May cause loss of consciousness, though not always 1
• Often characterized by a shift toward higher frequencies in EMG recordings compared to voluntary muscle contractions 2

Differentiating from Other Seizure Types

Tonic vs. Tonic-Clonic Seizures

• Tonic seizures involve only the rigid phase without the subsequent rhythmic jerking (clonic) movements 1
• Tonic-clonic seizures begin with rigidity but progress to rhythmic jerking movements 1
• EMG patterns differ: tonic seizures show increased frequency of signal, while tonic-clonic seizures show increased amplitude 2

Tonic vs. Atonic Seizures

• Atonic seizures involve sudden loss of muscle tone (flaccidity) rather than increased tone 1
• Atonic seizures are rare and typically occur in children with pre-existing neurological problems 1

Tonic vs. Focal Seizures with Preserved Awareness

• Some focal seizures may present with tonic posturing that is asymmetrical or limited to one side 3
• Patients may retain awareness during these focal tonic seizures 3

Clinical Significance and Outcomes

Tonic seizures may indicate:

• Epilepsy syndromes, particularly generalized epilepsy 4
• Possible structural brain abnormalities in some cases 1
• Potential metabolic triggers such as hypocalcemia (especially in patients with conditions like 22q11.2 deletion syndrome) 1

The prognosis varies:

• In children, primary generalized tonic seizures often have a favorable prognosis similar to generalized tonic-clonic seizures 5
• In adults with new-onset tonic seizures, especially during acute illness, they may respond well to antiepileptic monotherapy 6

Diagnostic Approach

When evaluating a patient with suspected tonic seizures:

1. Obtain detailed eyewitness accounts of the event, focusing on:

   • Presence of rigidity without rhythmic jerking
   • Duration of unconsciousness (typically <30 seconds in syncope, longer in seizures) 1
   • Whether movements began before or after loss of consciousness 1

2. Consider EEG monitoring to capture the event and confirm the diagnosis 1, 6

   • Video EEG can help differentiate tonic seizures from non-epileptic events

3. Evaluate for potential triggers such as:

   • Hypocalcemia or hypomagnesemia 1
   • Structural brain abnormalities 1
   • Medication effects 1

Common Pitfalls and Caveats

• Tonic seizures may be misdiagnosed as syncope with posturing 1
• Brief tonic seizures might be confused with cataplexy (sudden loss of muscle tone triggered by emotions) 1
• Focal tonic seizures with preserved awareness might be mistaken for psychogenic non-epileptic seizures, especially if voluntary movements occur during the episode 3
• Movements during syncope are typically asynchronous and limited, occurring after the person has fallen, while tonic posturing in epilepsy may occur before the fall 1

Remember that accurate identification of seizure type is crucial for appropriate treatment selection and management of underlying causes.