To investigate the potential misdiagnosis of Acute Nutritional Axonal Neuropathy (ANAN) as Guillan-Barré Syndrome (GBS) and identify distinguishing clinical and laboratory features.

ANAN is an underrecognized form of axonal polyneuropathy associated with nutritional deficiency. Its clinical presentation often mimics GBS, making accurate diagnosis and treatment challenging.

A retrospective chart review identified adults with GBS diagnosis at two main affiliated hospitals from 2019 to 2024. These cases were reviewed for diagnostic accuracy, and reclassified as confirmed GBS, possible ANAN (presence of risk factors for ANAN), and probable ANAN (documented vitamin deficiency with compatible presentation). Demographics, nutritional risk factors, clinical, laboratory, and electrodiagnostic data were analyzed. Probable ANAN cases were compared with confirmed GBS to identify distinguishing features.

Among 80 patients initially diagnosed with GBS, 26 cases (32.5%) were reclassified as possible ANAN (n=10, 12.5%) or probable ANAN (n=16, 20%). Among probable ANAN cases, most common nutritional deficiency was vitamin B12 (n=8), followed by vitamin E (n=4), thiamine (n = 3), and combined folate and B6 deficiency (n=1). Compared with confirmed GBS, probable ANAN cases had similar mean age (51.3 vs. 52.0 years, p = 0.933), sex distribution (62.5% vs. 50% female, p = 0.409), and cerebrospinal fluid albuminocytologic dissociation, but significantly higher rates of prior bariatric surgery (31.2% vs. 0%, p < 0.001), alcoholism (50% vs. 11%, p = 0.002), and axonal nerve conduction study (NCS) pattern (100% vs. 27%, p<0.001). Almost all patients received IVIG or PLEX treatment (100% vs. 96%, p = 0.9).

Approximately one-fifth of patients initially diagnosed with GBS were more consistent with ANAN after comprehensive review. Features associated with ANAN include alcoholism, prior bariatric surgery, and axonal NCS. Recognizing ANAN as a nutrition-related mimic of GBS may improve diagnostic accuracy and prevent unnecessary immunotherapy.