The book differentiates between several types of catatonia, which have different features, clinical courses, prognoses, genetic patterns, and responses to treatment. I found the classification schemes confusing. Some differentiate between "excited" and "retarded" forms of catatonia. "Periodic catatonia," often not recognized by clinicians, has a cyclical pattern and has strong genetic transmission. "Systematic" catatonias can be more chronic. "Malignant catatonia," possibly related to NMS, can have a high mortality rate, especially if treated with neuroleptic medications.