Correspondence (letter to the editor): Olfactory Hallucinations

The term “phantosmias” reflects the current guideline on olfactory dysfunction from the German Society of Oto-Rhino-Laryngology, Head and Neck Surgery, as mentioned in the review article. The definition “sensation of smells in the absence of a stimulus” is also identical with that in the S2 guideline (1), but it would also correspond to olfactory hallucinations. “Trick of the senses without external stimulus” defines hallucinations. This is of direct clinical relevance, because such symptoms may indicate further psychiatric/neurological diagnoses not mentioned in the article—especially if a patient reports these to their physician as the dominant symptom in the initial consultation (as experience has shown). So the issue is not only one of nomenclature but one of potential consequences for the planned revised edition of the ear, nose, and throat medicine guideline (1).

Olfactory hallucinations, or phantosmias, (in older people too) should prompt thoughts about further psychiatric disorders with hallucinations (mostly experienced as disagreeable, more rarely as agreeable), such as schizophrenia, depression, hallucination of one’s own (unpleasant) body odor, and temporal lobe epilepsy. In—severe—depression, olfactory hallucinations (for example, in the shape of a sensation of a smell of decay) are possible, and they may also be the consequence of olfactory dysfunction (3): “Owing to these limitations many patients with olfactory dysfunction show signs of depression.” But olfactory hallucinations may also occur in psychiatric disorders, independently of the presence of actual physical otolaryngological causes (for example, in the absence of an injury to the olfactory epithelium). The guideline for ear, nose, and throat medicine (1) mentions “neurological or psychiatric cause(s)” under 3.2.5. In general it seems that patients with long-term hallucinations (especially those in whom a clear somatic cause has not been identified) require psychotherapy, in close cooperation with the treating physicians who treat the somatic symptoms in parallel.

It is worth mentioning that, on the one hand, the sense of smell is often impaired in schizophrenia, and that, on the other hand, several studies (2) have found that up to a third of schizophrenia patients suffer from olfactory hallucinations.