Independently, the term periodic catatonia is sometimes used in modern literature to describe a syndrome of recurrent phases of acute catatonia (excited or inhibited type) with full remission between episodes, which resembles the description of "motility psychosis" in the Wernicke-Kleist-Leonhard school. System catatonias or systematic catatonias are only defined in the Wernicke-Kleist-Leonhard school. These are chronic-progressive conditions characterized by specific disturbances of volition and psychomotricity, leading to a dramatic decline of executive and adaptive functioning and ability to communicate. They are considered forms of schizophrenia but distinct from other schizophrenic conditions. Affective flattening and apparent loss of interests are common but may be related to reduced emotional expression rather than lack of emotion. Heredity is low. Of the 21 different forms (6 "simple" and 15 "combined" forms) that have been described, most overlap only partially - if at all - with current definitions of either catatonia or schizophrenia, and thus are difficult to classify according to modern diagnostic manuals. Early childhood catatonias are also a diagnosis exclusive to the Wernicke-Kleist-Leonhard school, and refers to system catatonias that manifest in young children. Clinically, these conditions resemble severe regressive forms of autism. Chronic catatonia-like breakdown or Autistic catatonia refers to a functional decline seen in some patients with pre-existing autism spectrum disorder and/or intellectual disability which usually runs a chronic-progressive course and encompasses attenuated catatonic symptoms as well as mood and anxiety symptoms that increasingly interfere with adaptive functioning. Onset is typically insidious and often mistaken for background autistic symptoms.
Those with hypoactive delirium present with similarly to retarded catatonia, withdrawn and quiet. However, catatonia also includes other distinguishing features including posturing and rigidity as well as a positive response to benzodiazepines. Patients with locked-in syndrome present with immobility and mutism; however, unlike patients with catatonia who are unmotivated to communicate, patients with locked-in syndrome try to communicate with eye movements and blinking. Furthermore, locked-in syndrome is caused by damage to the brainstem. Stiff-person syndrome and catatonia are similar in that they may both present with rigidity, autonomic instability and a positive response to benzodiazepines. However, stiff-person syndrome may be associated with anti-glutamic acid decarboxylase (anti-GAD) antibodies and other catatonic signs such as mutism and posturing are not part of the syndrome. Untreated late-stage Parkinsons disease may present similarly to retarded catatonia with symptoms of immobility, rigidity, and difficulty speaking. Further complicating the diagnosis is the fact that many patients with Parkinsons disease will have major depressive disorder, which may be the underlying cause of catatonia. Parkinsons disease can be distinguished from catatonia by a positive response to levodopa. Catatonia on the other hand will show a positive response to benzodiazepines. Extrapyramidal side effects of antipsychotic medication, especially dystonia and akathisia, can be difficult to distinguish from catatonic symptoms, or may confound them in the psychiatric setting. Extrapyramidal motor disorders usually do not involve social symptoms like negativism, while individuals with catatonic excitement typically do not have the physically painful compulsion to move that is seen in akathisia.