Catatonic features are observed in many psychiatric conditions. Primary catatonia, in which a person has the syndrome and no evidence of another disorder, is a hypothesized condition, but is not established. The clinical challenge is to recognize catatonia and the condition that causes it. In this chapter, we describe the differential diagnosis of disorders that underlie the expression of catatonia, and syndromes that simulate and may be mistaken for it.

“The duck principle” is a fundamental tenet of diagnosis: if it looks, walks, and quacks like a duck, it is a duck. The tenet is applicable to the diagnosis of catatonia. If a patient exhibits catatonic features, it is best to consider the patient as having catatonia. If features seem isolated from a clear underlying cause or are inconclusive, catatonic features can be temporarily relieved with an intravenous sedative, such as lorazepam or amobarbital. An intravenous injection of 1–2 mg lorazepam (0.5 mg/ml) or up to 500 mg amobarbital (50 mg/ml) over two minutes should relieve mutism, posturing, and rigidity. (At this rate of injection, laryngospasm is not a problem.) During the injection, talk to the patient, even if he is mute.