inability to ambulate; diminished vibration; pain in his lower limbs; diffuse hypokinesis without infarction scarring, or infiltrate; non-ischemic cardiomyopathy; a patient received a double dose influenza vaccine; Guillain-Barre syndrome/ acute inflammatory demyelinating polyradiculopathy; dysphagia; mild dysarthria; proximal muscle weakness; could not lift his arms above his head; Initial information was received on 28-Aug-2021 regarding an unsolicited valid serious case from the other healthcare professional issued in a literature article.  This case involves a 79 years old male patient who experienced dysphagia, mild dysarthria (dysarthria), proximal muscle weakness (muscular weakness), inability to ambulate (mobility decreased), could not lift his arms above his head(joint range of motion decreased), diminished vibration (decreased vibratory sense), pain in his lower limbs (pain in extremity), diffuse hypokinesis without infarction scarring, or infiltrate (hypokinesia), non-ischemic cardiomyopathy (cardiomyopathy) and developed Guillain-Barre syndrome/ acute inflammatory demyelinating polyradiculopathy (Guillain-Barre syndrome), after receiving double dose of INFLUENZA VACCINE (extra dose administered).  The patient had no medical history or recent illness.  The patient's past medical treatments, vaccinations, concomitant medication, and family history were not provided.  On an unknown date, the patient received a double dose of suspect INFLUENZA VACCINE (produced by unknown manufacturer, batch number and expiry date were not reported) via an unknown route at an unknown administration site for prophylactic vaccination respectively.  On an unknown date, the patient experienced serious symptoms of dysphagia, mild dysarthria (dysarthria), proximal muscle weakness (muscular weakness), inability to ambulate(mobility decreased), could not lift his arms above his head(joint range of motion decreased), diminished vibration (decreased vibratory sense), pain in his lower limbs (pain in extremity), diffuse hypokinesis without infarction scarring, or infiltrate (hypokinesia), non-ischemic cardiomyopathy (cardiomyopathy) and developed Guillain-Barre syndrome (GBS) / acute inflammatory demyelinating polyradiculopathy (Guillain-Barre syndrome) which was diagnosed (two weeks), following the administration of INFLUENZA VACCINE. These events were assessed as medically significant.  Intensity of event dysarthria was mild.  It was also a case of an actual medication error due to extra dose administered (latency: same day).  Laboratory test results included: Physical exam demonstrated diminished vibration and pain in his lower limbs and 0 to 1 plus deep tendon reflexes throughout without myalgias. Complete blood count (CBC)/ Basic Metabolic Panel (BMP) were unremarkable. Notable labs included creatinine kinase 274 U/L (unit/liter) (30-170 U/L), lactate 2.4 mmol/L (mole/cubic meter) (0.67-1.8 mmol/L), and troponin 0.33 µg/L (microgram/liter) (0-0.5 µg/L). Infectious workup was negative. Family was unaffected. A lumbar puncture revealed protein 45 mg/dL (milligrams per deciliter) (15-60 mg/dL). Head and spine imaging were unremarkable. Transthoracic echocardiogram (TTE) showed left ventricular ejection fraction (EF) of 20-25 percent and apical, anterolateral, anteroseptal and inferoseptal wall motion abnormalities. Electromyography (EMG) suggested an axonal demyelinating polyneuropathy but was not diagnostic. Autoimmune workup was negative. Repeat EMG showed a sensorimotor polyneuropathy with demyelination without myopathic components, confirming acute inflammatory demyelinating polyradiculopathy. Cardiac Magnetic resonance imaging (MRI) with gadolinium revealed diffuse hypokinesis without infarction, scarring, or infiltrate, suggesting potential for functional recovery.  The patient was treated with two doses of IMMUNOGLOBULINS Intravenous (IVIG) for Guillain-Barre syndrome via intravenous route. Guideline directed medical therapy was initiated for non-ischemic cardiomyopathy with reduced EF.  After resuming IVIG for 5 total days of treatment, patient displayed improvement and transferred to inpatient rehabilitation 15 days after symptom onset.   Impact/ Discussion: This case illustrates an unusual presentation of GBS and the need to rapidly initiate appropriate treatment. Proximal weakness remains atypical. Rapidly developing profound weakness was also uncharacteristic, as maximum disability typically takes weeks. Mechanism of myocyte injury in rhabdomyolysis from GBS was unclear. Myocardial involvement varies in severity and appears reversible. Cardiomyopathy in GBS appears rare and incidence remains unknown. Proposed mechanisms for GBS-related cardiomyopathy include autonomic and nervous dysfunction from immune-mediated nerve damage. Mainstay of GBS treatment is prompt IVIG infusion.   Conclusion: 1. Clinicians should be aware that hyper acute onset of proximal weakness, myositis, and cardiomyopathy are atypical features of GBS. 2. Cardiovascular involvement of GBS may be severe yet reversible with appropriate treatment.  The causality of the suspect with the events were reported as GBS and influenza vaccinations have been temporally correlated, but little evidence supports a causal relationship. It is unclear if a double dose vaccination confers greater risk.  This suspected adverse reaction report is submitted and classified as a medication error solely and exclusively to ensure the marketing authorization holder's compliance with the requirements set out in the Directive 2001/83/EC and Module VI of the Good Pharmacovigilance Practices. The classification as a medical error is in no way intended, nor should it be interpreted or construed as an allegation or claim made by the marketing authorization holder that any third party has contributed to or is to be held liable for the occurrence of this medication error.  Information on the batch number was requested for this case.; Sender's Comments: This case involves a 79 years old male patient who experienced Guillain-Barre syndrome, dysphagia, dysarthria, muscular weakness, mobility decreased, joint range of motion decreased, decreased vibratory sense, pain in extremity, hypokinesia, cardiomyopathy two weeks after receiving INFLUENZA VACCINE (unknown manufacturer). Electromyography confirmed acute inflammatory demyelinating polyradiculopathy. The time to onset is compatible. The patient's medical condition at time of vaccination, concomitant medication and other lab test ruling out alternate etiologies were not reported. Based upon the reported information, the role of vaccine cannot be assessed.