Analysis Of Pain Characteristics Of Acute Motor Axonal Neuropathy

Objective:Guillain-Barré syndrome(GBS)is an important cause of acute flaccid paralysis and is characterized by symmetrical weakness of the limbs,and hyporeflexia or areflexia.The two main subtypes of GBS are acute inflammatory demyelinating polyneuropathy(AIDP)and acute motor axonal neuropathy(AMAN).AMAN was identified in northern China in the 1990 s.Patients with AMAN generally have pure motor neuropathy and clinicians usually do not link pain with AMAN.Early studies thus only reported pain in AIDP.More recent studies did not illustrate the frequency and location of pain in AMAN clearly as well.The characteristics of pain in AMAN need to be further defined.Here we report a retrospective study defining the character,location,and intensity of pain in AMAN and AIDP in acute phase.Methods:In this retrospective study,44 patients with Guillain-Barré syndrome(GBS)having progressive weakness of more than one limb from December 2016 to September2020,were reviewed.The information,including the demographic characteristics,preceding infections,clinical symptoms and signs,severity at nadir,the characteristics of pain,use of analgesics,laboratory and electrophysiological data,and the medical treatment for GBS,were collected from the medical records and for statistical analysis.The diagnosis of AMAN and AIDP was according to the Hadden’s electrodiagnostic criteria.The severity of pain was roughly assessed by whether patients complained of difficulty in sleep due to pain.Results:In 44 patients,40.9%(18/44)were diagnosed as AMAN,34.1%(15/44)as AIDP,6.8%(3/44)as acute motor sensory axonal neuropathy(AMSAN),and 18.2%(8/44)were classified as equivocal.There were no statistically significant differences between AMAN and AIDP except for the ratios of cranial nerve involvement(P = 0.038),sensory loss(P < 0.001),respiratory support at nadir(P = 0.033),and serum IgM or IgG reactivity against GM1(P = 0.048).Pain was more prevalent in AMAN(76.5%)than in AIDP(26.7%,P = 0.02).Low back and extremities were the common locations of pain in AMAN(7/13 and 7/13,respectively)and AIDP(2/4 and 2/4,respectively).The severity of pain was comparable between AMAN and AIDP manifested by difficulty sleeping due to pain(3/13 vs.1/4,p=1).Six patients with AMAN and one patient with AIDP took analgesic medication,primarily for low back and muscle pain.Of these,monotherapy with gabapentin or celecoxib had a poor analgesic effect in five.The other two patients,both with AMAN,responded well to a combination of analgesics,such as gabapentin,duloxetine and ibuprofen.Previous studies indicated that autonomic involvement was rare in patients with AMAN.However,the results of our study revealed a similar prevalence between AMAN(22.2%)and AIDP(26.7%,P> 0.05).Particularly,bladder dysfunction(3/18)was the most common syndrome in AMAN.Conclusion:In traditional view,pain is rare in AMAN.Clinicians usually do not link pain with a pure motor neuropathy.Our study revealed a high prevalence of pain and first investigated the prevalence of low back pain in acute stage of AMAN.The presence or absence of pain is not useful for distinguishing AIDP from AMAN.Moreover,Autonomic involvement is not rare in AMAN patient.