Olfactory hallucinations in primary headache disorders: case series and literature review

Olfactory hallucinations (phantosmias) have rarely been reported in migraine patients. Unlike visual, sensory, language, brainstem, and motor symptoms, they are not recognized as a form of aura by the International Classification of Headache Disorders.

We examined the clinical features of 39 patients (14 new cases and 25 from the literature) with olfactory hallucinations in conjunction with their primary headache disorders.

In a 30-month period, the prevalence of phantosmias among all patients seen at our headache center was 0.66%. Phantosmias occurred most commonly in women with migraine, although they were also seen in several patients with other primary headache diagnoses. The typical hallucination lasted 5-60 minutes, occurred shortly before or simultaneous with the onset of head pain, and was of a highly specific and unpleasant odor, most commonly a burning smell. In the majority of patients, phantosmias diminished or disappeared with initiation of prophylactic therapy for headaches.

We propose that olfactory hallucinations are probably an uncommon but distinctive form of migraine aura, based on their semiology, timing and response to headache prophylaxis.