Clinical Features in Russian Patients with COVID-Associated Parosmia/Phanthosmia

Olfactory dysfunction is a typical symptom of COVID-19 infection. While COVID-associated anosmia is well-described, knowledge of parosmia (olfactory distortions) and phanthosmia (olfactory hallucinations) is relatively lacking. We undertook a clinical study of the parosmia/phanthosmia phenotype, aiming to support improved prediction and management of these symptoms.

In a cross-sectional study between September 2020 and May 2021, we recruited 187 COVID-19 patients with parosmia/phanthosmia via social media and a matched healthy control group from neurologists. The patients received an online video-consultation with a neurologist trained in olfactory research and completed a questionnaire to assess the nature of their subjective olfactory disorder.

In the acute period of COVID-19 parosmia/phanthosmia, patients often experienced comorbid manifestations such as fatigue, fever, headache, myalgia, and "brain fog". Isolated phanthosmia was observed in 13.9% of acute COVID-19 patients, as compared to 34.2% in the long term. Parosmia was described in 89.8% of patients in the long-term course of the disease. COVID-associated parosmia/phanthosmia was more common in women (81.3%) than men (18.7%). Almost all parosmia/phanthosmia patients had an acute history of anosmia, which often progressed to hyposmia. A third of the patients had a history of taste disturbance The long-term COVID-19 sequelae such as fatigue, brain fog, and dizziness are significantly more common among patients with parosmia/phanthosmia, as were autonomic symptoms such as awareness of heartbeat and rapid pulse. The incidence of migraine with aura was significantly higher in the parosmia/phanthosmia group than in the control group (8% versus 0.9%). The allergy was reported significantly more frequent in the study group compared to the control group.

Qualitative olfactory disorders occur frequently in COVID-19 patients. Those with the parosmia/phanthosmia phenotype have a higher risk for other symptoms, notably headache (including migraine with aura), fatigue, brain fog, dizziness, and cardiovascular/autonomic manifestations, as well as allergy. We suppose that further investigation of this phenomenon will reveal phenotypic variants depending on particular symptoms cluster; improved nosology of qualitative olfactory disorders in COIVD-19 is a prerequisite for establishing appropriate treatments.