Changes in smell can be a sign of COVID-19 and Lyme disease
Patients with COVID-19 often report changes in smell, including a loss of smell. In fact, an estimated 80% of patients have smell disturbances. “Smell loss is so common in people with the disease that some researchers have recommended its use as a diagnostic test because it may be a more reliable marker than fever or other symptoms,” writes Sutherland in Scientific America. 
According to Parma and colleagues, “A sudden loss of smell [and] taste is consistent with the now typical presentation of COVID-19 symptoms, it is highly probable that COVID-19 infection is the main reason of their smell and taste change.” 
The loss of smell is not unique to COVID-19. Patients with other illnesses, including Lyme disease, frequently report the same phenomenon. An impaired or heightened sense of smell has been described in patients suffering from neurological disorders, like Alzheimer’s and Parkinson’s disease,  autoimmune diseases,  fibromyalgia,  and Lyme disease. 
A decreased sense (hyposmia) or loss of smell has been described in patients diagnosed with fibromyalgia. These patients had “significantly lower thresholds of smell compared to healthy controls,” writes Amital et al. 
Meanwhile, another study found that 50% of 16 patients with Lyme disease suffered from hyperosmia (heightened sense of smell) versus none of the 18 control subjects. 
“The high prevalence of this olfactory disorder found in our study suggests the need for further studies of olfactory function in [Lyme] disease,” conclude the authors.  The loss of smell reported in COVID-19 patients is also a common symptom of Lyme disease. Click To Tweet
Other researchers report similar findings. Fallon et al. described a hypersensitivity in photophobia, sound sensitivity, touch, taste, and smell. “Foods may taste abnormally sour and bitter,” he writes. “Smells may seem overly intense and noxious.” 
Other chemosensory disturbances
Parma and colleagues found that COVID-19 patients can also present with other chemosensory disturbances. The chemosensory system refers to the body’s perception of chemical signals by the senses, particularly the perception of taste and smell.
“These results show that COVID-19-associated chemosensory impairment is not limited to smell, but also affects taste and chemesthesis [chemical sensitivity of the skin and mucous membranes].” 
The number of cases, however, were limited. “We found little incidence of qualitative changes in olfactory function, with only a small percentage of participants reporting distorted smells (consistent with parosmia) or phantom smells (consistent with phantosmia).”
Additional chemosensory disturbances included:
- Anosmia: The loss of the ability to detect one or more smells.
- Hyposmia: A decreased sensitivity to some or all smells.
- Ageusia: The loss of taste functions of the tongue, including sweetness, sourness, bitterness, saltiness.
- Hypogeusia: The reduced ability to taste things.
- Parosmia: Distortions of the sense of smell, including the inability to correctly identify odors.
- Dysgeusia: A distortion of the sense of taste.
- Phantosmia: Smelling something that is not actually there.
- Phantogeusia: A metallic or salty taste in the mouth for no reason.
Editor’s note: It is important to consider Lyme disease as a potential cause of sensory disturbances.
- Sutherland S. Mysteries of COVID Smell Loss Finally Yield Some Answers. Scientific America, November 18, 2020. https://www.scientificamerican.com/article/mysteries-of-covid-smell-loss-finally-yield-some-answers1/
- Parma V, et al. More Than Smell-COVID-19 Is Associated With Severe Impairment of Smell, Taste, and Chemesthesis. Chem Senses. 2020 Oct 9;45(7):609-622.
- Carlo Perricone, et al. Smell and autoimmunity: a comprehensive review. Clin Rev Allergy Immunol. 2013 Aug;45(1):87-96.
- Howard Amital, et al. Olfactory impairment in patients with the fibromyalgia syndrome and systemic sclerosis. Immunol Res. 2014 Dec;60(2-3):201-7. doi: 10.1007/s12026-014-8573-5.
- Puri BK, et al. Hyperosmia in Lyme disease Arq. Neuro-Psiquiatr. 2014 vol.72 no.8.
- Fallon BA, et al. The neuropsychiatric manifestations of Lyme borreliosis. Psychiatric Quarterly. Spring 1992,Vol 63, No 1.
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