To expose a potential Acute inflammatory demyelinating polyradiculoneuropathy (AIDP) mimicker and understand the significance of diagnostic tests in a case of Bannwarth syndrome. 

Lyme borreliosis is an infectious disease affecting the skin, nervous system, and joints transmitted by the bite of Ixodes Ricinus. Neurological manifestations occur in 3-15% of the cases. Bannwarth syndrome is reported in 3% of the CDC-verified cases of Lyme disease. It presents early within weeks to a few months of initial infection, mainly characterized by painful polyradiculoneuritis.

Case: A 67-year-old male presented with progressive bilateral upper extremity weakness, sparing the lower extremities with diffuse areflexia, facial diplegia, dysarthria, dysphagia, and diplopia. 

Initial exam was remarkable for bilateral arm weakness with left-sided lower motor neuron facial palsy and dysarthria. Symptoms quickly worsened to facial diplegia and dysphagia with inability to manage secretions. Magnetic resonance imaging (MRI) brain showed hyperintensity with enhancement of the left cerebellum and cauda equina enhancement on MRI lumbar spine. Cerebrospinal fluid (CSF) analysis was remarkable for elevated protein (448 mg/dl), mild pleocytosis (8/mm³), and albumin cytological dissociation. Monoclonal protein IgG kappa was present in the gamma globulin region. History, exam and initial work-up led to a tentative diagnosis of pharyngeal-cervical-brachial variant of AIDP. He was treated with plasmapheresis with mild improvement. Initial Lyme serum and CSF serology were positive with a positive confirmatory CSF western blot. His inpatient electromyography exposed asymmetric, subacute cervical polyradiculopathy with signs of active axonal denervation and reinnervation changes with no acquired demyelination. The patient was started on intravenous Ceftriaxone and physical therapy with significant improvement. 

Lyme disease is a magnificent chameleon; hence it is crucial to keep it among the differential diagnosis. This case emphasizes the importance of EMG amongst diagnostic tools given it ultimately, in combination with Lyme testing, changed the diagnosis and management for the patient.