The Neuropsychiatric Effects of CNS Structural Abnormalities (NECSA) classification: An aid to differential diagnosis

To the Editor

Complex diagnostic questions are often encountered when psychiatric symptoms present in the setting of neurologic disorders. Multiple pathogenetic factors need to be considered, but due to time constraints, clinicians tend not to approach the diagnostic process by working through algorithms of conditional probabilities. Instead, they tend to use mental shortcuts relying on pattern recognition (Ely et al., 2011). This time-saving heuristic approach comes at the expense of increased vulnerability to errors arising from a variety of cognitive biases (Croskerry, 2002, 2003). In a discipline as complex as neuropsychiatry, this can result in misattribution of psychiatric, cognitive and/or behavioral symptoms to a single cause when other differentials have not been considered—which impacts upon the choice of treatment.

Ely et al. (2011) argue that the most common cause of diagnostic error is failure to consider the correct diagnosis as a possibility, which can be addressed by differential diagnosis checklists. To optimize potential utility, such a checklist would benefit from being conceptually clear, easy to recall and time-efficient to apply.

The author proposes the Neuropsychiatric Effects of Central Nervous System (CNS) Structural Abnormalities (NECSA) classification. For neuropsychiatric symptoms in the context of any neuroimaging abnormality, the clinician is prompted to consider the five following potential pathogenetic effects—each of which would have different management implications. The same acronym ‘NECSA’ also serves as a mnemonic for the five pathogenetic effects.

1. (N)etwork disruption. The structural abnormality such as encephalomalacia, gliosis or a tumor (in addition to associated edema, ischemia or hydrocephalus) is thought to cause disruption in a functional network leading to psychiatric, cognitive and/or behavioral symptoms.

2. (E) lectrical overactivity. The structural abnormality acts as a focus for partial seizures which lead to neuropsychiatric symptoms.

3. (C) hemical (endocrine) overactivity. A secreting tumor (e.g. of the pituitary or hypothalamus) causes hormonally mediated neuropsychiatric effects.

4. (S) ide effects of treatment: Medication, surgery or radiotherapy used to address the original abnormality results in neuropsychiatric symptoms that occur independently of, or in addition to, any potential effects from the original lesion.

5. (A) djustment reaction: The psychological reaction triggered by the patient’s learning of the neurologic diagnosis, which might be influenced by premorbid psychopathology. The letter ‘A’ also serves as a reminder to consider (A)lternative contributors to the patient’s neuropsychiatric symptoms independent of the structural abnormality. Obviously, not all patients’ presentations will necessarily be entirely, or even partially, attributable to an identified structural lesion.

It is hoped that this classification will be useful to clinicians as a time-efficient aid to the systematic consideration of a broader range of pathogenetic factors for neuropsychiatric symptoms in the presence of a neuroimaging abnormality.