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In March 2020, WHO declared Covid-19 outbreak pandemic. There has been increasing evidence that frail, old, multi-pathological patients are at greater risk of developing severe Covid-19 infection than younger, healthy ones. Covid-19's impact on Parkinson's Disease (PD) patients could be analysed through both the influence on PD patients' health and their risk of developing severe Covid-19, and the consequences of lockdown and restrictive measures on mental and cognitive health on both patients and caregivers. Moreover, there are critical issues to be considered about patients' care and management through an unprecedented time like this. One important issue to consider is physiotherapy, as most patients cannot keep exercising because of restrictive measures which has profoundly impacted on their health. Lastly, the relationship between PD and Sars-Cov2 may be even more complicated than it seems as some studies have hypothesized a possible Covid-19-induced parkinsonism. Hereby, we review the state of the art about the relationship between Covid-19 and Parkinson's Disease, focusing on each of these five points.

According to the classical view, the cerebellum has long been confined to motor control physiology; however, it has now become evident that it exerts several non-somatic features other than the coordination of movement and is engaged also in the regulation of cognition and emotion. In a previous diffusion-weighted imaging-constrained spherical deconvolution (CSD) tractography study, we demonstrated the existence of a direct cerebellum-hippocampal pathway, thus reinforcing the hypothesis of the cerebellar role in non-motor domains. However, our understanding of limbic-cerebellar interconnectivity in humans is rather sparse, primarily due to the intrinsic limitation in the acquisition of in vivo tracing. Here, we provided tractographic evidences of connectivity patterns between the cerebellum and mammillary bodies by using whole-brain CSD tractography in 13 healthy subjects. We found both ipsilateral and contralateral connections between the mammillary bodies, cerebellar cortex, and dentate nucleus, in line with previous studies performed in rodents and primates. These pathways could improve our understanding of cerebellar role in several autonomic functions, visuospatial orientation, and memory and may shed new light on neurodegenerative diseases in which clinically relevant impairments in navigational skills or memory may become manifest at early stages.

We tested the hypothesis that fatigue in MS is related to a dysfunction in cortical areas involved in movement preparation. Thirty-three patients with clinically definite MS (16 with fatigue MS-F, 17 without fatigue MS-NF) and a relapsing-remitting course, matched for disease severity and duration, disability scores and level of depression were enrolled. They underwent a combined assessment with magnetic resonance imaging (MRI) and transcranial magnetic stimulation (TMS) and, for the electrophysiological study, were compared with 12 healthy controls. MRI was used to assess regional and total lesion-load volume (LL) on T1- and T2-weighted sequences and total brain volume on T1-weighted sequences. With TMS we tested central motor conduction time, short intracortical inhibition (SICI) and facilitation (ICF), pre-movement facilitation related to a simple reaction time paradigm and the effect of short trains of 5-Hz repetitive TMS (rTMS). No significant differences were found in total and regional LL between MS-F and MS-NF, except for a significant increase in frontal lobe LL in MS-F. Neurophysiological assessment did not disclose any difference of SICI and ICF among the three groups. The significant increase of MEP size produced by 5 Hz rTMS in controls was absent in both MS-NF and MS-F. MS-F lacked pre-movement facilitation compared with MS-NF and controls. The lack of pre-movement facilitation and the increased frontal lobe lesion load were significantly correlated to the FSS score, suggesting that central fatigue in MS is probably due to a dysfunction of cortical motor areas involved in movement preparation.

A 22-year-old patient presented with attacks of paroxysmal dystonia characterised by involuntary and uncontrollable movements affecting lower and upper limbs with sustained turning or twisting of the trunk. These motor paroxysms were induced by voluntary movements and lasted between 10 and 15 s with a frequency of 1-5 attacks per day. Transcranial magnetic stimulation of the motor cortex was found to induce motor paroxysms very similar to the spontaneous attacks. To evaluate motor cortex and brainstem excitability immediately after and between the attacks, a neurophysiological study was performed.

We describe a reflex evoked in neck muscles by stimulation of afferent fibres in the trigeminal nerve. The clearest responses were seen in averaged, unrectified, monopolar surface electromyographic (EMG) recordings from active sternocleidomastoid muscles after stimulation of the infraorbital nerve. They consisted of a bilateral positive/negative (p19, n31) wave with a mean onset latency of 12.9 ms which corresponded to a period of inhibition in the underlying motor unit activity. Responses also could be seen in splenius and trapezius, but not in arm muscles. Stimuli to other branches of the trigeminal nerve (supraorbital or mental) did not produce such clear effects. The threshold for the reflex was relatively low (2-4 times perceptual threshold) and its size scaled with the level of background EMG in an approximately linear fashion. Responses to infraorbital stimulation did not interact with other short-latency inhibitory responses in the sternocleidomastoid muscle evoked by loud acoustic clicks or stimulation of the median nerve at the wrist. We suggest that the infraorbital response is part of a head withdrawal reflex involving an oligosynaptic trigemino-cervical system similar to that described in the cat.