Olfactory hallucination in childhood primary headaches: case series.

Background: Although olfactory hallucination (OH) has been reported in patients with primary headaches, olfactory aura has not been recognised by the International Classification of Headache Disorders (ICHD-2). In this study, we examined the frequency and characteristics of OH among children and adolescents with primary headaches.

Methods: 839 neurologically normal patients with primary headaches (537 migraine) were eligible for the assessment of olfactory hallucination. Headache diagnosis was based on the ICHD. Data were prospectively collected during clinic sessions and using headache diaries.

Results: Olfactory hallucination was reported exclusively during headache attacks by 21/839 (2.5%) patients, all of whom had migraine. The prevalence of olfactory hallucination was 3.9% among migraineurs (6.5% among those with migraine aura). Olfactory hallucination shortly followed the onset of headaches and lasted from 15 to 50 minutes. Of those with MA, 10 patients had visual aura; two had somatosensory aura; one had motor aura; and two had a combination of visual and somatosensory aura. Using the ICHD-2, both OH and migraine aura occurred in the same headache attacks. In 12/15 patients, OH occurred simultaneously with migraine aura, whereas in 3/12 patients, it preceded aura.

Conclusion: Our findings show that olfactory hallucination occurs in migraine and it has similarities to migraine aura.