Discussion
PTS is the classic presentation of the brachial plexus inflammation, involving the long thoracic, subscapular, superficial radial and anterior interosseous nerves, but can also involve other peripheral nerves, lower brachial plexus and phrenic nerves(1)(6).
PTS is a not a rare neurological disorder as previously thought(1). A recent prospective study suggests that its actual incidence rate is 1 per 1000 per year(7). It is most likely underdiagnosed due to its misleading manifestations (6).
In general, the idiopathic form of PTS occurs mainly in men with a sex ratio of 2 and a median age of 40 years. It is typically characterized by the onset of sudden severe shoulder pain, developing paresis and tingling within several hours to days later, as reported in our case(6).
The diagnosis of PTS is primarily clinical, there is no specific diagnostic test (1). ENMG may lack sensitivity and accuracy in confirming the diagnosis(6). In our case, the pattern brachial plexus neuritis comforted the diagnosis hypothesis. In fact, this sign is only found in 30 to 45% of confirmed PTS cases(4). Shoulder MRI helpsexcluding differential diagnoses such as intrinsic shoulder disorder. Our patient showed no signal abnormalities.
The exact mechanism in PTS is still unknown but multiple factors are involved. The immunological hypothesis is plausible by the fact that 50% of PTS patients have a history of a trigger event such as infection, vaccination, surgery, pregnancy, physical or mental stress(4). Concomitant hepatitis E viral infection was found in 10% of patients which pleads in favor of an infectious or post-infectious mechanism(4). In peripheral nerve biopsy, epineural perivascular mononuclear T-cell infiltration was found(6) which supports the immunological theory.
In this regard, our case is interesting as the symptoms’ onset occurred after a vaccination: Covid-19 BNT162b2 mRNA vaccine (manufactured by Pfizer).
Post vaccination PTS is very rare(8). PTS onset occurs within 28 days after vaccination, in an estimated 4.3–15.5% of cases(9). Our patient typically developed classic symptoms of PTS 15 days after receiving the second dose of BNT162b2 mRNA vaccine, as it was reported in the literature.
Concerning covid-19 vaccines, and after at least one dose, 56 reports of PTS were detected by The Vaccine Adverse Event Reporting System (VAERS) in July 2021, among which 24 reports concerned BNT162b2 mRNA vaccine(9).
To date, there is no specific treatment for PTS. Support therapy including corticosteroids, analgesics, immobilization and physical therapy are the milestone of PTS treatment, as it was highlighted in our case(4). No recommendations have been established due to the lack of Randomized Controlled Trials. Intravenous corticosteroids and immunoglobulins can be used in severe extensive PTS with intense pain in order to minimize symptoms duration and recover functional abilities(4).
Outcomes are heterogenous and depend on the phase in which the patient is diagnosed, the intensity of pain, the extent of plexus involvement and whether the symptoms are bilateral or unilateral(10).