Migraine Symptoms: Olfactory Hallucinations

When we think of Migraine aura, the visual aura symptoms most commonly come to mind. In their diagnostic criteria for "typical aura," the International Headache Society (IHS) states that the typical aura consists of at least one of the following:

  1. fully reversible visual symptoms including positive features (e.g., flickering lights, spots or lines) and/or negative features (i.e., loss of vision)
  2. fully reversible sensory symptoms including positive features (i.e., pins and needles) and/or negative features (i.e., numbness)
  3. fully reversible dysphasic speech disturbance4

There are, however, other possible aura symptoms that have not made their way into the IHS criteria. One of these symptoms is olfactory hallucinations (phantosmias), which is smelling odors that aren't really present.

Coleman et al examined the features of 25 cases from medical literature. They also reviewed patient records from more than 2,100 patients seen at the Montefiore Headache Center over a 30-month period and found 14 cases (just under 7%) where patients had described smelling scents during their headaches or Migraines.

The objective of their study was:

"to gain a greater understanding of this phenomenon by performing a detailed analysis of the aggregated patients reported in the literature and those encountered at our center, which treats a diverse urban patient population as well as a large number of regional and national referrals. We also aimed to estimate the prevalence of phantosmias across all primary headache disorder patients evaluated at our center."2

They hypothesized that:

  1. most headache patients experiencing phantosmias have migraine,
  2. phantosmias have similar semiology (symptoms or signs) to other aura types in their timing and evolution, and
  3. phantosmias become less frequent with prophylactic therapies aimed at suppressing the underlying headache disorder.2

Of the 39 patients with olfactory hallucinations identified:

  • 33 patients (84.6%) had Migraine,
  • three patients (7.7%) had cluster headaches,
  • one patient had hemicrania continua, and
  • one patient had chronic daily headache.

Dr. Brian Grosberg summarized the findings of this study in a conversation I had with him:

"Phantosmias, or olfactory hallucinations, can rarely be a part of the aura that some people experience before a Migraine attack. About 20-25% of people with recurrent Migraines have an aura that precedes or accompanies their headaches. Unlike visual, sensory, and language auras, disturbances in the sense of smell (i.e., olfactory hallucinations) have not been recognized as part of Migraine aura. My colleagues and I think this is because olfactory hallucinations have not been commonly reported. We found that only 0.7% of our patients described smelling scents in conjunction with their headaches. It's certainly uncommon, but it is distinctive. Usually, the olfactory hallucinations are not sweet. The most scents are either burning or smoky. Some headache sufferers described a general burning smell, while other said they smelled cigar smoke, wood smoke or burned popcorn. After those burning scents, "decomposition" odors like garbage or sewage were the next most common. A few people did describe pleasant odors, including the scent of oranges or coffee."5

Study summary:

Coleman et al. state:

"In summary, phantosmias are an uncommon but distinct manifestation of headache disorders. They occur predominately in women with migraine and are usually readily identifiable and unpleasant, with burning the single most common odor described. Their semiology, timing and response to headache prophylaxis suggest that they deserve strong consideration as a form of aura."2

Wrapping it up

Although not listed as an aura symptom by the IHS, olfactory hallucinations have been shown to occur as a Migraine aura symptom. Most olfactory hallucinations aren't pleasant scents; they're either burning or smoky. or odors such as garbage or sewage. A smaller number of patients describe pleasant odors.

Dr. Grosberg said, "It's certainly uncommon, but it is distinctive." I suspect that olfactory hallucinations aren't as uncommon as they seem. I suspect that patients don't report them because they're not specifically asked about them and haven't associated them with their Migraines. If a Migraineur has no other aura symptoms, they may even have been diagnosed with and think they have Migraine without aura. We've seen this with Migraine prodrome where patients think they don't experience the prodrome until they're asked about specific prodrome symptoms.

This is an area that could use more research, and I agree with the authors that olfactory hallucinations deserve consideration by the IHS as a form of aura.

Have you ever had olfactory hallucinations with your Migraines?

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