The esoteric nature of conversion disorder symptoms makes it difficult to delineate their precise etiology. The onset of such disorders is often described as psychogenic in origin. Two prominent theories may explain the generation of symptoms demonstrated in conversion disorders. The psychoanalytic theory, also known as the Freudian theory, posits that physical symptoms arise from unconscious conflicts between an instinctual impulse (eg, aggression or sexuality) and barriers toward expressing that impulse.[5] As a result of this theoretical unconscious conflict, physical symptoms manifest in a way that symbolically reflects that conflict. An example of this might include a presentation of vaginismus, or involuntary contraction of the vagina, alleged to result from repressed sexual impulses. By contrast, the learning theory focuses on the characterization of physical symptoms as classically conditioned learned behaviors. In this paradigm, physical symptoms serve as a coping mechanism to psychological stressors.[5]
Certain biological and neuropsychological factors have been associated with the onset of conversion disorder. An example of such factors include distinct changes in brain structure and function. For instance, impaired hemispheric communication within the brain has been observed in patients with conversion disorder. This impaired hemispheric communication is thought to contribute to excessive cortical arousal, giving rise to discrete physical symptoms.[5] One meta-analysis of neuroimaging studies of patients with conversion disorder found evidence of altered cortical structure compared with healthy control subjects. Additionally, decreased pituitary gland volume was observed in patients with nonepileptic seizures.[6]
Conversion disorders are entirely distinct from the similar syndromes of factitious disorders and malingering. Factitious disorders feature the falsification or induction of physical or psychological symptoms for the purpose of presenting an illness or syndrome in the absence of other obvious external rewards. In a sense, a person likes or wants the role of being a patient. By comparison, malingering is the similar false production or exaggeration of symptoms motivated by external incentives (eg, avoiding work, financial compensation, obtaining medications).[7] However, in noting these distinctions, obtaining evidence that symptoms are feigned or not feigned is often difficult and unreliable.
The diagnosis of conversion disorder requires that "clinical findings provide evidence of incompatibility between the symptom and recognized neurologic or medical conditions."[1] Such evidence of incompatibility between symptoms present and known conditions may be potentially obtained through several clinical signs. For example, the Hoover sign, an involuntary extension of the leg upon flexion of the contralateral leg, can help distinguish organic from nonorganic hemiparesis. Similarly, the entrainment test can aid in identifying functional tremors.[7]
Noting again that conversion disorder is a diagnosis of exclusion, clinicians must consider alternative causes of the symptoms present. In particular, primary neurologic disease must be excluded through the careful examination of the progression of symptoms. Therefore, in the diagnosis, the physician must first rule out any and all possible physical etiologies. This often leads to extensive testing; however, missing a medically treatable cause is likely worse.
Conditions that are similar to conversion disorder, such as somatic symptom disorder, must either be ruled out or recognized as being comorbid with the conversion disorder.[8] In both conversion disorder and somatic symptom disorder, the symptoms present do not have an obvious medical cause. A distinction is that the diagnosis of conversion disorder requires that the symptoms present are incompatible with typical medical or neurologic disease. By contrast, somatic symptom disorder symptoms are frequently compatible with possible pathophysiology.[1]
Mood disorders, such as major depressive disorder, are frequently comorbid with conversion disorder. Depressive disorders may produce limb weakness similar to what might be seen in some conversion disorders. However, a depressive disorder generally includes more generalized weakness than the focal signs that are often more typical for those associated with a conversion disorder.[9]Anxiety disorders, such as panic disorder, are also known to produce transient neurologic symptoms similar to those that might be seen in a conversion disorder. Such symptoms are typically more acute and short-lived compared with those of conversion disorder.[9]
The workup of conversion disorder also may include evoked potentials (EPs). EPs are measurable electrical impulses conducted by the nervous system in response to certain stimuli.[10] Functional abnormalities can alter EP readings in known ways. Such EP alterations can indicate functional abnormalities in visual, auditory, or sensory pathways. However, given the nonorganic nature of conversion symptoms, EP readings in patients with conversion disorder are typically normal.[11]
In this patient, visual EPs (VEPs) are needed to confirm the diagnosis of visual loss. VEPs can be measured in several ways. They are often measured with a VEP pattern reversal test that uses a checkerboard stimulus.[12] This, combined with normal neuro-ophthalmic findings, strongly suggests a diagnosis of functional vision loss.[13] Additionally, electromyography tests must also be conducted to evaluate the lower-extremity weakness in presentations similar to the patient's in this case.
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Cite this: Jeffrey S. Forrest, Alexander B. Shortridge. A 23-Year-Old With Blindness After a Fall She Can't Remember - Medscape - Nov 27, 2019.