What evidence gives clues to the physiological basis for conversion disorder?
It's usually important to rule out other medical conditions when considering many psychiatric diagnoses due to similarities in symptoms between them. There are many examples but I'm not sure if it's appropriate to note them here as a lot of symptoms have to be considered in a clinical context and might be mistaken as medical advice. It's also important to note that concurrent medical and psychiatric conditions frequently occur with individuals diagnosed with conversion disorder.(2).

Conversion disorder was previously combined with somatisation disorder and was known as hysteria.(2). Conversion disorder is a diagnosis of exclusion where the symptoms are not a result of:


neurological or other medical condition;
the effect of a substance; or 
cultural behavior or experience.(1).


The key is that these are not intentionally or medically driven symptoms but rather physical manifestations of psychological needs ("unconscious manifestations of emotional conflict"(3)). Psychoanalytic theory suggests that "conversion disorder is caused by repression of unconscious intrapsychic conflict and conversion of anxiety into a physical symptom"(2).

In terms of physiological basis of conversion disorder, it's been suggested that an imbalance in metabolism between the dominant and non-dominant brain hemispheres; and impaired communication between the two may be an issue.(2). There are some other points you can also read at MedScape.


Ferri. Ferri's Clinical Advisor. 2012. Mosby.
Sadock. Kaplan &amp; Sadock's Synopsis of Psychiatry. 10th ed. 2007. Wolters Kluwer.
Jacobson. Psychiatric Secrets. 2nd ed. 2001. Hanley and Belfus.