Semiology

The Value of Semiology

The word semiology comes from the Greek σημεῖον meaning a mark, a sign, or a portent. Similar ideas are present in the concepts of semiotics which is a study of signs and sign systems.

Semiology refers to the sequence of symptoms experienced by a patient having a seizure. This may be as simple as a single event: clonic jerking of an extremity for instance.

You may have heard of seizures such as complex partial seizures or tonic-clonic seizures. These are more concise terms for classes of seizures that have some common properties. They are not very precise for determing the semiology of a patient’s seizure. In fact, patients can experience multiple seizure “types” within the same ictal event. They may start with a funny feeling in the stomach (a simple partial seizure), then lose responsiveness with the environment and have fumbling movements with the hand (a complex partial seizure), and then evolve into a convulsive seizure after that. These are not separate seizures. They are all part of the same event; the initial ictal discharge evolves and spreads and affects different parts of the brain and in so doing effects different semiologies.

The language of semiology can seem daunting and strange at first. It is a different set of jargon from that encountered in general neurology and has its own idiosyncrasies and pitfalls. Here is a good glossary of ictal semiology terms from a 2001 ILAE task force. It reflects much of the semiologic seizure classification scheme formulated by Hans Lűders and others from Ohio in the 1990s and later.

It is a worthwhile truism to state that whatever the brain can do, a seizure can do. Seizures can cause both positive and negative phenomena. They can force a movement or sensation that wouldn’t have occurred or they can interfere with a normal function and degrade it. Often the effect is both positive and negative: a simple visual aura both produces a hallucinatory perception and interferes with normal vision in the area affected.

The truism works moreso as a caution against automatically determining that any strange semiology is automatically “functional” or “psychogenic.” Plenty of phenomena that look like dissociative attacks can end up being caused by an ictal discharge even if it is deep or hidden. Suspicion is always warranted and video-EEG almost always casts some light on the process. Where vEEG doesn’t help, it can almost never hinder the correct diagnosis. This is true even for scalp EEG-negative phenomena; the experienced neurophysiologist or epileptologist will know when a semiology warrants search for deeper ictal discharges, as with iSPECT or MEG.

Semiology is often the first clue uncovered by the physician as to the epileptogenic zone of the patient. In the office, an informed history-taker can draw from the patient or from eyewitnesses at least a coarse description of the semiology.

Taking a semiology history