Acute Small Fiber Neuropathy With Severe Autonomic Dysfunction at the Interface of Guillain–Barré Syndrome

Guillain-Barr syndrome (GBS) is the most widely recognized cause of acute flaccid paralysis and is typically characterized by progressive, symmetrical limb weakness and absent or reduced deep tendon reflexes, primarily affecting large myelinated fibers. 1 Although pain and autonomic dysfunction are not uncommon during the course of GBS, whether acute small fiber neuropathy is another disease variant remains controversial. 2 We report a patient who presented with acute postinfectious neuropathy predominantly involving small fiber impairment, illustrating the diagnostic interface between these two entities.A 42-year-old male visited our emergency room with a 3-day history of progressive leg weakness and urinary retention.He had no past medical history but had experienced the common cold 10 days before coming to the hospital.The initial neurological examination revealed bilateral, symmetric, segmental weakness in his legs (especially the hip flexors, at MRC grade 4/4) and hyperactive deep tendon reflexes.Ankle clonus and the Babinski sign were absent, and a sensory examination was normal across all modalities.An abdominal examination revealed distension of his lower abdomen and residual urine at 823 mL, suggesting bladder retention.Whole-spine MRI did not reveal any intramedullary or compressive lesion.The results of a nerve conduction study (NCS), including late responses, were normal.Cerebrospinal fluid (CSF) showed normal pressure and white blood cell count, but elevated protein (99 mg/dL).Under the diagnosis of GBS, intravenous immunoglobulin (IVIG) was administered at 2 g/kg over 5 days, during which his lower limb weakness improved rapidly.On hospital day 2, he complained of orthostatic dizziness, headache, abdominal bloating, and a burning pain and electrical shock-like sensation on his foot.His systolic blood pressure fluctuated between 90 and 180 mm Hg.Brain MRI indicated high signal intensities without enhancement in the cortical and subcortical areas of the left occipital polar region, suggestive of posterior reversible encephalopathy syndrome.Autonomic function tests revealed severe cardiovagal impairment with sympathetic adrenergic and cholinergic impairment, and quantitative sensory testing showed significantly elevated thresholds to cold and heat pain perceptions, suggestive of small fiber neuropathy (Fig. 1).The results of an NCS performed 1 week later were normal.The results of laboratory tests performed to differentiate other causes of small-fiber neuropathy were all within the normal ranges, including diabetes mellitus, Sjgren's syndrome, vitamins B6 and B12, thyroid function, human immunodeficiency virus, hepatitis C, paraneoplastic antibodies, and cancer screening.Antibodies to IgM and IgG gangliosides (GM1, GD1a, and GQ1b) and ganglionic acetylcholine receptor were all negative.The patient's symptoms stabilized within 4 weeks, and he slowly recovered over a period of about 3 months with supportive care.This patient represents a case of acute postinfectious neuropathy characterized by prominent pain and autonomic impairment documented with objective small fiber impairment