Anosmia in the context of "Parkinson's"

Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor and non-motor systems. The motor symptoms are collectively called parkinsonism and include tremors, bradykinesia (slowness in initiating movement), rigidity, and postural instability (difficulty maintaining balance). Non-motor symptoms such as dysautonomia (autonomic nervous system failures), sleep abnormalities, anosmia (decreased ability to smell), and behavioral changes or neuropsychiatric problems, such as cognitive impairment, psychosis, and anxiety, may appear at any stage of the disease. Symptoms typically develop gradually and non-motor issues become more prevalent as the disease progresses.

Most Parkinson's disease cases are idiopathic, though contributing factors have been identified. Pathophysiology involves progressive degeneration of nerve cells in the substantia nigra, a midbrain region that provides dopamine to the basal ganglia, a system involved in voluntary motor control. The cause of this cell death is poorly understood, but involves the aggregation of alpha-synuclein into Lewy bodies within neurons. Other potential factors involve genetic and environmental influences, medications, lifestyle, and prior health conditions.

The symptoms of COVID-19 are variable depending on the type of variant contracted, ranging from mild symptoms to a potentially fatal illness. Common symptoms include coughing, fever, loss of smell and taste, with less common ones including headaches, nasal congestion and runny nose, muscle pain, sore throat, diarrhea, eye irritation, and toes swelling or turning purple, and in moderate to severe cases, breathing difficulties. People with the COVID-19 infection may have different symptoms, and their symptoms may change over time.

Three common clusters of symptoms have been identified: a respiratory symptom cluster with cough, sputum, shortness of breath, and fever; a musculoskeletal symptom cluster with muscle and joint pain, headache, and fatigue; and a cluster of digestive symptoms with abdominal pain, vomiting, and diarrhea. In people without prior ear, nose, or throat disorders, loss of taste combined with loss of smell is associated with COVID-19 and is reported in as many as 88% of symptomatic cases.

Coronavirus disease 2019 (COVID-19) is a contagious disease caused by the coronavirus SARS-CoV-2. In January 2020, the disease spread worldwide, resulting in the COVID-19 pandemic.

The symptoms of COVID‑19 can vary but often include fever, fatigue, cough, breathing difficulties, loss of smell, and loss of taste. Symptoms may begin one to 14 days after exposure to the virus. At least a third of people who are infected do not develop noticeable symptoms. Of those who develop symptoms noticeable enough to be classified as patients, most (81%) develop mild to moderate symptoms (up to mild pneumonia), while 14% develop severe symptoms (dyspnea, hypoxia, or more than 50% lung involvement on imaging), and 5% develop critical symptoms (respiratory failure, shock, or multiorgan dysfunction). Older people have a higher risk of developing severe symptoms. Some complications result in death. Some people continue to experience a range of effects (long COVID) for months or years after infection, and damage to organs has been observed. Multi-year studies on the long-term effects are ongoing.

Ageusia (from negative prefix a- and Ancient Greek γεῦσις geûsis 'taste') is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami (meaning 'savory taste'). It is sometimes confused with anosmia – a loss of the sense of smell. True ageusia is relatively rare compared to hypogeusia – a partial loss of taste – and dysgeusia – a distortion or alteration of taste.

Even though ageusia is considered relatively rare it can impact individuals of any age or demographic. There has been an increase in reported cases of ageusia, due to the COVID-19 pandemic making ageusia more commonly diagnosed than before.

Hyposmia, or microsmia, is a reduced ability to smell and to detect odors. A related condition is anosmia, in which no odors can be detected. Some of the causes of olfaction problems are allergies, nasal polyps, viral infections and head trauma. In 2012 an estimated 9.8 million people aged 40 and older in the United States had hyposmia and an additional 3.4 million had anosmia/severe hyposmia.

Hyposmia might be a very early sign of Parkinson's disease. Hyposmia is also an early and almost universal finding in Alzheimer's disease and dementia with Lewy bodies. Lifelong hyposmia could be caused by or comorbid with Kallmann syndrome or autism. Along with other chemosensory disturbances, hyposmia can be a key indicator of COVID-19.

Long COVID or long-haul COVID is a group of health problems persisting or developing after an initial period of COVID-19 infection. Symptoms can last weeks, months or years and are often debilitating. The World Health Organization defines long COVID as starting three months after the initial COVID-19 infection, but other agencies define it as starting at four weeks after the initial infection.

Long COVID is characterised by a large number of symptoms that sometimes disappear and then reappear. Commonly reported symptoms of long COVID are fatigue, memory problems, shortness of breath, and sleep disorder. Several other symptoms, including headaches, mental health issues, initial loss of smell or taste, muscle weakness, fever, and cognitive dysfunction may also present. Symptoms often get worse after mental or physical effort, a process called post-exertional malaise. There is a large overlap in symptoms with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).

Vitamin B₁₂ deficiency, also known as cobalamin deficiency, is the medical condition in which the blood and tissue have a lower than normal level of vitamin B₁₂. Symptoms can vary from none to severe. Mild deficiency may have few or absent symptoms. In moderate deficiency, feeling tired, headaches, soreness of the tongue, mouth ulcers, breathlessness, feeling faint, rapid heartbeat, low blood pressure, pallor, hair loss, decreased ability to think and severe joint pain and the beginning of neurological symptoms, including abnormal sensations such as pins and needles, numbness and tinnitus may occur. Severe deficiency may include symptoms of reduced heart function as well as more severe neurological symptoms, including changes in reflexes, poor muscle function, memory problems, blurred vision, irritability, ataxia, decreased smell and taste, decreased level of consciousness, depression, anxiety, guilt and psychosis. If left untreated, some of these changes can become permanent. Temporary infertility, reversible with treatment, may occur. A late finding type of anemia known as megaloblastic anemia is often but not always present. In exclusively breastfed infants of vegan mothers, undetected and untreated deficiency can lead to poor growth, poor development, and difficulties with movement.

Causes are usually related to conditions that give rise to malabsorption of vitamin B₁₂ particularly autoimmune gastritis in pernicious anemia. Other conditions giving rise to malabsorption include surgical removal of the stomach, chronic inflammation of the pancreas, intestinal parasites, certain medications such as long-term use of proton pump inhibitors, H2-receptor blockers, and metformin, and some genetic disorders.