Hallucinated scents such as a burning or rotten smell, or even the scent of foie gras, can be a part of the “aura” that some people perceive before a migraine attack, although it is rare, according to a U.S. study.
About 30 percent of people with recurrent migraines have sensory disturbances shortly before their headache hits, known as aura, but these are usually visual, such as flashes of light or blind spots. Tingling sensations or numbness, or difficulty speaking or understanding language, may also appear.
But the study, conducted by Matthew Robbins and colleagues at the Montefiore Headache Center in New York, found that a small number of people described smelling scents in conjunction with their headaches.
“It’s uncommon, but distinctive,” said Robbins, noting that disturbances in the sense of smell, known as olfactory hallucinations, have not been covered in a systematic review of medical literature before.
Researchers reviewed 25 reported cases of patients with headaches, migraines in most cases, and olfactory hallucinations. They also examined records from more than 2,100 patients seen over 30 months. Fourteen people, or just under 0.7 percent, had described smelling scents ahead of their headaches.
Olfactory hallucinations in primary headache disorders: Case series and literature review
Background: 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.
Methods: 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.
Results: 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.
Conclusions: 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.
Elisheva R Coleman
Brian M Grosberg
Matthew S Robbins
Albert Einstein College of Medicine, USA
“The most common was of the burning or smoke variety,” Robbins said.
Some sufferers described a general burning smell. others said they smelled cigar smoke, wood smoke or burned popcorn.
“Decomposition” odors, such as garbage or sewage, were the next most common smell reported. A few people described pleasant odours, including the scent of oranges, coffee or, in one case, foie gras.
About 11 percent of the world’s population suffers from migraines, so even though olfactory hallucinations are an unusual part of aura, there could still be a fairly large number of people who experience them, Robbins said.
Auditory Hallucinations Associated with Headaches Following Traumatic Brain Injury
Traumatic brain injury (TBI) can lead to significant neurological damage, and is strongly associated with chronic headaches, seizure disorder, cognitive impairment, sleep disorders, and psychiatric disorders. The prevalence of such impairments in TBI patients appears to be quite high, with >20% of patients experiencing at least some neurocognitive deficits that can persist for decades. Over 1 million cases of TBI occur every year and often disable otherwise young and healthy patients, making a significant impact on healthcare as a whole.
The prevalence of certain psychiatric disorders following TBI has been extensively studied, and it is now known that head trauma is associated with substantial increases in depression, anxiety, and personality disorders. Psychosis due to TBI (PDTBI) is another less common psychiatric diagnosis made in patients who exhibit hallucinations or delusions following a significant head injury. This is a difficult diagnosis to make, since the clinician must decide whether the psychosis can be better explained by other psychiatric disorders that may have incidentally occurred in spite of the injury.
Jadon Webb, MD, PhD, John Quinn, MD and Arthur Westover, MD
It’s not clear why the hallucinated odors are most often unpleasant, or why they are only rarely part of migraine aura.
But aura symptoms are thought to involve a phenomenon called “cortical spreading depression,” where a wave of increased electrical activity in nerve cells of the brain is followed by a wave of depressed activity, Robbins said.
That same phenomenon might underlie olfactory hallucinations – and because the brain’s smell centres occupy much less space than its sight centres, that could, in theory, explain why phantom scents are so much less common, he added.
It is also possible that some people with migraines and olfactory hallucinations do not recognize the phenomenon, he added. People know something is wrong when they see zigzag lines, but it is easy to assume a small is actually coming from somewhere.
Since some disorders, such as Parkinson’s disease, can cause a person to smell scents that are not present, any such hallucinations without an accompanying headache should be checked out, he warned.