We read with interest the review article by Paliwal et al. about the neuromuscular manifestations of neuro-COVID [1]. It has been concluded that peripheral nervous system (PNS) disease in COVID-19 includes myalgia, myositis/rhabdomyolysis, myasthenia gravis, Guillain-Barre syndrome (GBS), neuropathy, olfactory/gustatory dysfunction, and neuropathy of cranial nerves [1]. The study is attractive but raises concerns that should be discussed.
We disagree with the number of PNS abnormalities triggered by SARS-CoV-2 infections. Not only the abnormalities reported in the results belong to neuro-COVID of the PNS, but also disorders such as plexopathy (Parsonage-Turner syndrome), myasthenic syndrome, small fiber neuropathy, dermatomyositis, and vasculitis of the PNS.
We also disagree with the classification of the PNS anormalies. Myalgia is a symptom and not a neurological condition. Myalgia is non-specific and can occur without a specific neurological condition being diagnosed. However, myalgia can also be a manifestation of myositis, vasculitis, or rhabdomyolysis.
We disagree cranial nerve (CN) involvement in SARS-CoV-2 infections includes only CN-I, CN-II, CN-III, CN-IV, CN-V, and CN-VI [1]. With the exception of the accessory nerve, all other CNs can be involved in SARS-CoV-2 infections. Vestibulo-cochlear nerve neuritis was reported in a pregnant Moroccan female six weeks after the onset of SARS-CoV-2 [2]. Vestibular neuronitis has been reported as a complication of a SARS-CoV-2 infection in a 60yo male [3]. Involvement of CN-IX and CN-X has been particularly reported in GBS patients but also without involvement of the peripheral nerves. Involvement of the hypoglossal nerve has been observed in connection with SARS-CoV-2 associated polyneuritis cranialis [4].
With regard to the olfactory or gustatory dysfunction in SARS-CoV-2 infections, it is still unclear whether it is due to involvement of the central nervous system (CNS) or the peripheral nervous system (PNS). There are even indications that it could only be due to direct affection of the taste buds or olfactory cells.
What is missing from the review is the involvement of the autonomic nervous system. Autonomic dysfunction is a common finding in SARS-CoV-2 infected patents and can be due to interference with the peripheral or central part of the sympathetic or parasympathetic pathways.
It lacks the neuromuscular complications caused by anti-SARS-CoV-2 drugs or drugs used to treat COVID-19 patients in the intensive care unit. These drugs can cause toxic neuropathy, critical ill neuropathy,/myopathy, (e.g. chloroquine), or rhabdomyolysis (e.g. azithromycin, hydroxy-chloroquine, placitaxel, propofol, imastinib, piperacillin, meropenem, hydrochlorothiazide, and acetaminophen). It has been also reported that chloroquine causes myasthenic syndrome in individual patients [5].
Secondary neuropathies due to involvement of organs other than the lungs, such as the kidneys (e.g. renal neuropathy) or pancreas (e.g. diabetic neuropathy) were not discussed.
Overall, the interesting study has some shortcomings that call the results and their interpretation into question. Clarifying these weaknesses would strengthen the conclusions and could add value to the study. PNS involvement in neuro-COVID is more widespread than expected.