A stroke is a medical emergency that occurs when blood flow to a part of the brain is interrupted, either by a blockage (ischemic stroke) or bleeding (hemorrhagic stroke). This loss of oxygen and nutrients causes brain cells to die quickly, which can lead to lasting damage or death. While most people are familiar with the common signs of stroke, such as sudden weakness or facial drooping, some less common neurological symptoms affect the sense of smell. Understanding these unusual symptoms provides insight into the brain’s complex functions, but they should never distract from recognizing the primary, universally known signs of a stroke.
Olfactory Hallucinations (Phantosmia)
A stroke does not cause the body to produce a specific odor, but it can cause the patient to perceive a smell that is not actually present. This phenomenon is known as phantosmia, or an olfactory hallucination. Phantosmia is relatively uncommon, accounting for only a small percentage of olfactory complaints. The phantom smells are most often described as unpleasant or foul, a condition sometimes called cacosmia. People frequently report smelling things like burnt rubber, smoke, chemicals, metallic odors, or rotting food. This sensation occurs because the stroke has disrupted the brain’s signaling processes, making the central nervous system register a smell signal without an external trigger.
Loss of Smell (Anosmia and Hyposmia)
A stroke can also cause a partial or complete loss of the sense of smell. A reduced ability to smell is medically known as hyposmia, while the complete inability to smell is termed anosmia. These deficits occur because the stroke has damaged the pathways or centers in the brain responsible for processing olfactory information. Studies show that olfactory dysfunction occurs frequently in chronic stroke patients. A significant number of stroke patients exhibit hyposmia, and a smaller percentage experience anosmia in the year following their stroke. This loss of smell can decrease the appreciation of food, leading to poor nutrition and a decrease in overall quality of life.
Neurological Basis of Smell Disturbances
The specific smell disturbance a person experiences depends on the location of the stroke within the brain. The sense of smell is processed in specific areas, including the olfactory cortex, which is primarily located in the temporal lobe, and parts of the frontal lobe. A stroke that affects the blood supply to these localized areas can interrupt or damage the neural circuitry. Phantosmia, the hallucination, is often linked to irritation or abnormal electrical activity within the olfactory cortex of the temporal lobe. Conversely, anosmia or hyposmia results from the destruction or damage of the olfactory pathways, such as a lesion in the frontal lobe’s orbitofrontal cortex, which is involved in translating smell signals.
Recognizing Primary Stroke Signs and Emergency Action
While changes in the sense of smell are rare, they should not be the primary focus for recognizing a stroke. The public must concentrate on the more common symptoms, which demand immediate emergency action. The most effective tool for rapid recognition is the F.A.S.T. mnemonic:
- Face drooping (one side of the face droops when smiling)
- Arm weakness (one arm drifts downward when both are raised)
- Speech difficulty (slurred speech or difficulty understanding language)
- Time to call emergency services
The “Time” component emphasizes the urgency of calling 911 immediately. Prompt treatment within a few hours of symptom onset significantly improves outcomes because every minute a stroke goes untreated results in the death of millions of brain cells, underscoring the principle that “time is brain.”