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).