A 69‐Year‐Old Male with Subacute Gait Disturbance—<i>Blastocystis hominis</i> Causing Extensive Colitis with Thiamine Deficiency

Blastocystis hominis is a worldwide, zoonotic anaerobic protozoan found in the colon and cecum of humans, pigs, monkeys, rodents, and poultry. It is present in vacuolar, ameboid, and cystic forms.1 In humans, it transforms from the vacuolar to the ameboid form as it passes through the intestine and is expelled in feces in cyst form, likely the infective stage.2 The deposited cysts could be hosted by animals and reinfect humans through contaminated water, food, or direct contact with human feces. First discovered in 1911, there is much debate about the pathogenicity of Blastocystis in humans; however, current reports indicate that it causes acute gastroenteritis3 and contributes to iron deficiency anemia.4 Nonetheless, neurological dysfunction caused by B. hominis infection is rarely reported. We report a Taiwanese man with subacute onset of cerebellar ataxia caused by B. hominis−induced extensive colitis and thiamine deficiency. A 69-year-old Taiwanese male, a pig farmer, with no family history of neurodegenerative or movement disorders, experienced subacute onset and progressive worsening of gait disturbance, tremors, and slurred speech for 1 month. Seven days ago, symptoms progressed to difficulty writing, hypersensitivity to sounds, increased anxiety, and visual hallucinations, including a yellowish hue over normal objects and distorted shapes. His cognition remained intact. He had been admitted for 3 days because of intermittent watery diarrhea for 1 month prior to the commencement of neurological symptoms. The situation improved after supportive treatment, but diarrhea recurred from time to time. He did not have limb numbness, dizziness, headache, nausea/vomiting, diplopia, or dysphagia. He had chronic hepatitis B infection, cholecystectomy, gastroesophageal reflux disease (LA grade A), and peptic ulcer, for which he had never undergone panendoscopy but was on the proton pump inhibitor treatment. Examination revealed pan-cerebellar dysfunction, including truncal titubation, limb dysmetria, ataxic gait, and slow saccades (Video 1). Brain MRI, electroencephalogram, cerebrospinal fluid (CSF) study, paraneoplastic antibodies, tumor markers, thyroid function, autoimmune and lipid profiles, and vitamin B12 levels were unremarkable. Nerve conduction study without electromyography showed slightly prolonged F-wave latency in bilateral tibial and peroneal nerves. Cognitive function test was intact. Serum IgE was elevated, although allergy testing was unremarkable. A further colonoscopy revealed extensive enterocolitis (Fig. 1A), and the stool culture was positive for B. hominis. We started with intravenous vitamin B complex, leading to improvement in pan-cerebellar syndrome within 3 days and marked progress by day 7. We then switched to oral Alinami-F (vitamins B1 and B2) (Alinamin Pharmaceutical Co., Ltd. Tokyo, Japan) with no recurrence of symptoms. Metronidazole was added for Blastocystis colitis. A follow-up colonoscopy 1 month later showed remission (Fig. 1B), and the clinical symptoms fully resolved (Video 2). B. hominis has been reported to cause colitis mimicking Clostridium difficile infection.5 Our case demonstrates that B. hominis−induced extensive colitis may lead to poor thiamin absorption, causing cerebellar dysfunction. The differential diagnosis of adult-onset subacute cerebellar ataxia includes paraneoplastic syndrome, inflammatory or immune-mediated disorders, malabsorption, and Whipple disease.6 The latter two also show diarrhea and abdomen pain. The pivotal step in the diagnosis of B. hominis in our case was the elevated serum IgE level and positive stool culture result, along with the patient's history of animal contact. Although the pathogenicity of B. hominis remains controversial and its response to metronidazole is variable,7 an increasing number of reports highlight its potential pathogenic role.5 The rapid clinical response and recovery from colitis further strengthen the causative link between the cerebellar dysfunction observed in the index case and B. hominis-induced colitis. Because the patient occasionally shared food with migrant workers in the pigsty, fecal-oral transmission is suspected. Extensive colitis increases the gut permeability that affects thiamine absorption. Thiamine is absorbed in the colon through active transportation, whereas vitamin B12 is absorbed through endocytosis.8 This is why our patient had a normal vitamin B12 serum level. Neurological manifestation of thiamine deficiency includes nystagmus, ophthalmoplegia, ataxia, and weakness. Cognitive impairment manifested as Wernicke–Korsacoff syndrome occurs in more severe cases.9 Based on the diagnosed certainty proposed by Infection-Related Movement Disorders (IRMD) Study Group consensus,10 our case was classified as possible IRMD. The patient had well-defined pan-cerebellar syndrome and an ongoing infection diagnosed by culture. This is the first case to link pan-cerebellar syndrome with B. hominis infection, highlighting the potential of B. hominis−induced colitis to cause thiamine deficiency and pan-cerebellar syndrome. The limitation of this study is that we could not check serum thiamine levels directly. However, prompt clinical improvement after therapeutic trial and resolution of enterocolitis by metronidazole confirm the diagnosis. Our case provides a new differential diagnosis of subacute cerebellar ataxia—thiamine deficiency caused by parasite infection. In the era of globalization, presumed rare infections may be introduced by individuals traveling from abroad. (1) Conception of the work: A. Organization, B. Execution; (2) Manuscript: A. Writing of the first draft, B. Review and critique. Y.C.T.: 1A, 1B, 2A M.E.: 1B, 2A C.H.L.: 1A, 2B We thank the patient for participating in the study. Ethical Compliance Statement: Written informed consent was signed by the patient in both English and Chinese. This case report was approved by the E-DA Hospital Institutional Review Board (IRB)—EMRP-113-117. We confirm that we have read the journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. Funding Sources and Conflicts of Interest: This case study was funded by E-DA Hospital Kaohsiung, Taiwan (grant number: EDAHS112037). All authors report no conflicts of interest. Financial Disclosures for the Previous 12 Months: All authors have no financial disclosures or conflicts of interest related to the manuscript. Data available on request due to privacy/ethical restrictions.