Post-Covid, are you suffering
from a persistent loss of smell?
We at the Kadri Center for Advanced Rhinology are aware that post-Covid complications are regrettably much more common than you might think. The Covid-19 pandemic has, in fact, caused thousands to suffer various traumatic post-infection chronic complications. For some of us, these complications have unfortunately developed into chronic or longer-term conditions. Loss of smell has been widely recognized as one of the most frequent and commonly reported symptoms. In fact, some studies have shown that post-Covid loss of smell can be as high as 60 percent! According to a recent medical study published in the Journal of Internal Medicine, 51 percent of 580 people who lost their sense of smell reported that they had not regained full function a five full months later. The study also reported that a longer-term loss (greater than six months) of smell due to Covid persists in about 5 percent of all Covid patients. Full loss of smell (Anosmia) or the partial loss of smell (Hyposmia) are oftentimes associated with an accompanying loss of taste (Dysgeusia).
Smell is an Underrated Sense
Our sense of smell can be as essential and enriching to our lives as our sense of sight, but we rarely contemplate a loss of this crucial sensory ability. Loss of smell was much less common before the advent of Covid-19. The reality is that many of us have now actually experienced the devastating effects of losing our sense of smell. We all recognize that a conscious perception of smell, and all the myriad motivational and emotional aspects associated with smell and scent memory are essential for a rich and rewarding life. Many of us feel the loss more deeply now that we can no longer experience a truly multi-variegated and robust sense of smell.
The Ability to Smell is Intrinsic to our Nature
This debilitating condition can often last for many months and may cause considerable distress to the patient. Loss of smell in any will negatively impact quality of life as our sense of smell is a source of daily enjoyment and fulfillment. A loss or diminishment of our sense of smell can cause food to be tasteless, and may dim or even eliminate poignant memories or the pleasing emotions that scent can conjure whenever we encounter the endless array of aromas that light up many of our brain’s pleasure centers. Our olfactory sense can revive long-dormant memories of joy or happiness. It can effortlessly register a multitude of pheromones that might trigger love or intimacy long before the rest of our brain has even formulated a single conscious thought. These acute sensory functions are controlled by those distinct parts of the brain that receive chemosensory signals which originate from within the olfactory system. Consequently, a long-term or qualitative reduction of our sense of smell (e.g. more than a few months) can result in episodic depression, anxiety and social isolation. For some of us, the loss of smell can be devastating.
How Does Smell Work?
Function, Anatomy and Pathology of the Olfactory Organs
Our sense of smell begins, as you might expect, with the nose itself. Unlike other cranial nerves whose origins begin within the brain stem, the olfactory nerve (first cranial nerve) instead originates from olfactory sensory neurons located in the roof of the nose under the cribriform plate. These nerve cells or neurons are clustered beneath the mucosa (located in the roof of the nasal vault).
Axons (nerve fibers) penetrate through the cribriform plate and enter the anterior cranial fossa to form olfactory bulbs. These axons create synaptic glomeruli when they interact with the neurons which then travel along the olfactory tract under the frontal lobe of the brain to reach specific areas of the olfactory cortex. Impulses from the olfactory nerve are then decoded after they have traveled to the frontal lobe of the brain eventually reaching the olfactory cortex. It is here and at this moment that these impulses from the olfactory nerve are registered as “smell”.
How Does Covid-19 Take Away Your Sense of Smell?
Infection and Damage to Critical Olfactory Support Cells
For patients experiencing loss of smell, the Covid-19 virus has typically infected, compromised and ultimately damaged crucial olfactory support cells. Sensory tissue located in the roof of the nasal cavity (well past the nostrils and behind the eyes), is called the olfactory epithelium. This sensory tissue contains nerve cells known as olfactory sensory neurons. These neurons actually detect inhaled odors and subsequently communicate that information to the brain itself. These same neurons (located in the olfactory mucosa) are intermingled with support (sustentacular) cells, blood vessel (vascular endothelial) cells and stem cells (basal cells). The support, blood vessel, and stem cells are all extremely susceptible to injury from physical, chemical, and, or biological agents such as Covid-19 (SARS-CoV2 or Corona Virus).
In a recent Harvard study, it was found that olfactory sensory neurons (located in the olfactory mucosa) don’t express the ACE2 receptor required by Covid-19 to enter human cells. However, ACE2 is expressed in the supporting cells, as well as in certain populations of blood vessel and stem cells. These are the very cells that support and maintain the olfactory sensory neurons found in the ofactory mucosa. So when Covid-19 invades and partially or completely kills these critical supporting cell populations, the virus disrupts relevant sensory neuron pathways resulting in Loss of Smell. And damage by Covid to these supporting and stem cells can sometimes be long-lasting or permanent as it also injures and infects surrounding blood vessels. This type of invasive viral interaction often leads to local inflammation or disruption of the olfactory epithelium tissue in other ways, too. Covid-19 can often impair or even prevent sensory neurons from performing their invaluable smell-related functions.
Can Covid-19 Cause Irreversible Loss of Smell?
For Some Patients, Loss of Smell (Anosmia) Can Last Much Longer, but is Often Reversible with Proper Treatment
Because recent research from Harvard indicates that Covid does not directly transfect (infect) the olfactory sensory neurons themselves, but instead, affects the function of the supporting (sustentacular) cells, it is typically unlikely to permanently damage the olfactory neural circuits. In most cases, therefore, persistent or permanent loss of smell is reparable. Patients usually find that once the Covid infection resolves, the olfactory neurons don’t appear to require rebuilding or replacement.
The Journal of Internal Medicine cited that among nearly 2,600 people with confirmed SARS-CoV-2 infection, olfactory dysfunction was prevalent in 85.9 percent of patient-reported mild COVID-19 cases, 4.5 percent in moderate cases, and 6.9 percent in severe-to-critical cases. The study also indicated that about 24 percent of patients did not recover their sense of smell 60 days after dysfunction began, 15.3 percent still showed deficiency at 60 days, and 4.7 percent had not recovered full olfaction (sense of smell) at six months.
Fortunately, data strongly suggests the while most Covid-19 patients recover their sense of smell over the course of weeks, some unfortunate patients do not regain satisfactory olfactory function within months, or in severe cases, ever.
If you think you may be one of these patients who have lost their smell due to Covid infection, or any other reason, and would like to know if your loss of smell may be reversible by our novel treatments, please click here to learn more about your treatment options.
Zain Kadri, M.D., F.A.C.S.
Kadri Center for
Advanced Rhinology
7677 Center Avenue
Suite 211
Huntington Beach, CA 92647