A 58–year old man was admitted to the Emergency Department with a chief complaint of weakness in the neck. 11 weeks before this presentation he required hospitalization because of viral pneumonia with a positive test of a nasopharyngeal swab for SARS-CoV-2 RNA. He subsequently developed respiratory insufficiency and sepsis needing mechanical ventilation, prone position, systemic steroids, anticoagulation and vasopressors. He began to respond and after 2 weeks he was extubated successfully. The patient was sent home with intensive physical therapy 4 weeks before the current presentation. On a follow up visit at the outpatient clinic after 8 weeks of the SARS-CoV-2 infection, he complained about having pain and discomfort on the neck with fatigue while walking.
On admission, the patient stated that he had ten days of weakness on his neck specially while standing (see video). The patient was still having intensive physical therapy. He denied having diplopia, dysphagia, dysphonia, fasciculations, cramps or weakness in other muscles. The medical history was unremarkable except for a diagnosis of asthma in childhood and the past history of viral pneumonia.
Relevant findings at the neurological evaluation include generalized hypotrophy and localized weakness of neck extensors (3), neck flexors (4), both deltoids (3) and both infraspinatus (3). Fatigability was present after exertion and he noticed weakness worsened in the afternoon. He could count until fifteen with a single maximal inspiration. Bedside measurements of PEF (positive expiratory force) and NIF (Negative inspiratory force) were 73 CmH20 and 59 CmH20 from predetermined values of 111 CmH20 and 208 CmH20 respectively.
He had normal initial laboratory analysis including: hemogram, renal function, electrolytes, thyroid function and creatine phosphokinase (CPK). No radicular enhancements, signs of myelopathy or soft tissue collection on cervical MRI were found. No abnormalities were seen in the nerve conduction study and electromyography (EMG).
Complementary studies with repetitive nerve stimulation (RNS) and single-fiber EMG (SFEMG) were performed. Trapezius and Nasalis RNS, showed a reduction >10% of the muscular action potential with the repetition of the stimulus (Fig. 1, panel A). SFEMG in the orbicularis oculi muscle revealed a mean consecutive difference of 64 µs, with 15 pairs (41%) having an outlier range jitter (Fig. 1, panel B). Thoracic and abdominal CT scans showed no evidence of thymoma or other space occupying lesions.
Fig. 1. Electro-diagnosis including RNS and SFEMF
Panel A. Slow RNS at 2-3 Hz with five stimuli at the trapezius muscle. Maximal Decrement is shown between the first and fourth compound muscle action potential (CMAP).
Panel B. SFEMF of the orbicularis oculi muscle. Recording shows variation of the triggering (signalled in green) and the slave potential (signalled in yellow) between fiber pairs indicating an increased Jitter.
A postsynaptic myasthenic syndrome was suspected and a trial of pyridostigmine was administered with clinical improvement. Binding antibodies against AChR in serum were elevated (56 pmol/l with a normal value <0.5 pmol/l) while MuSK antibodies were negative.