FISH’S Clinical Psychopathology

Organic hallucinations

Organic hallucinations can occur in any sensory modality and they may occur in a variety of neurological and psychiatric disorders. The focus in this section will be on the psychiatric causes.

Organic visual hallucinations occur in eye disorders as well as in disorders of the central nervous system and lesions of the optic tract. Complex scenic hallucinations occur in temporal lobe lesions. Charles Bonnet syndrome consists of visual hallucinations in the absence of any other psychopathology, although impaired vision is present. All the dementias as well as delirium and substance abuse are associated with visual hallucinations.

The phantom limb is the most common organic somatic hallucination of psychiatric origin. In this case the patient feels that they have a limb from which in fact they are not receiving any sensations either because it has been amputated or because the sensory pathways from it have been destroyed. In rare cases with thalamo−parietal lesions the patient describes a third limb.

In most phantom limbs the phenomenon is produced by peripheral and central disorders. Phantom limb occurs in about 95% of all amputations after the age of 6 years. Occasionally a phantom limb develops after a lesion of the peripheral nerve or the medulla or spinal cord. The phantom limb does not necessarily correspond to the previous image of the limb in that it may be shorter or consist only of the distal portion so that the phantom hand arises from the shoulder. If there is clouding of consciousness, the patient may be deluded that the limb is real. Equivalent perceptions of phantom organs may also occur after other surgical procedures such as mastectomy, enuleation of the eye, removal of the larynx or the construction of a colostomy. The person is aware of the existence of the organ or limb and describes pain or paraesthesia in the space occupied by the phantom organ and this persists in a minority of patients. When the experience is related to a limb the perception shrinks over time, with distal parts disappearing more quickly

than those that are proximal. Lesions of the parietal lobe can also produce somatic hallucinations with distortion or splitting-off of body parts.

Lesions of the temporal lobe are associated with multi-sensory hallucinations but they do not include somatic hallucinations, which is to be expected because the somatic sensory area is separated from the temporal lobe by the Sylvian fissure.