Hyponatremia is the most common fluid and electrolyte imbalance in hospitalized patients. Among hyponatremia causes, syndrome of inappropriate antidiuretic hormone secretion is a condition characterized by excessive release of antidiuretic hormone from the pituitary gland or nonpituitary sources. One of the most common drugs associated with hyponatremia is selective serotonin reuptake inhibitors, especially in elderly patients. Therefore, distinct therapeutic alternatives are essential for patients having risk factors for hyponatremia or syndrome of inappropriate antidiuretic hormone secretion development. The present article aims to review the available literature evaluating mirtazapine-induced hyponatremia or syndrome of inappropriate antidiuretic hormone secretion in adult or elderly patients in order to determine the incidence of these adverse effects and analyze the existence of any correlation between the administered dose of mirtazapine and serum sodium levels. A systematic search was conducted, using key terms from the research topic, their synonyms, and Boolean/logic operators. From this evidence pool, inclusion and exclusion criteria were applied. We abstracted population characteristics and clinical endpoints. Relevant data from selected studies was abstracted and subject to statistical analysis. A total sample size of 30,851 patients treated with mirtazapine was included. Mirtazapine-induced hyponatremia incidence was 3.26% (95% CI 3.06-3.45%), with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) the most probable underlying cause. Among case series and case reports evaluated (n=7), hyponatremia and SIADH were more frequent in female patients (71.4%) and the most frequent clinical manifestations included confusion (57%), somnolence (42%), and altered speech (28%). Mean serum sodium levels were (117 mEq/L, ranging from 113-130 mEq/L). The average time lapse between mirtazapine administration and clinical findings was 34 days. The Spearman's rank correlation coefficient between mirtazapine dosage and serum sodium levels was -0.3181 with a p-value >0.05. In conclusion, mirtazapine presents a moderate risk of hyponatremia and should be considered as an alternative therapy in patients requiring antidepressants with risk factors for this preventable adverse effect.

Guillain-Barré syndrome (GBS) represents the main cause of flaccid paralysis worldwide. Although most cases have a typical clinical presentation of symmetric ascending flaccid paralysis with areflexia or hyporeflexia, this disease may present as multiple clinical entities, therefore representing a diagnostic challenge for physicians, who should consider these variants when assessing neuropathies. The pharyngeal-cervical-brachial (PCB) variant of Guillain-Barré syndrome is defined by rapidly progressive oropharyngeal and cervicobrachial weakness associated with hyporeflexia or areflexia in the upper limbs. It is present in 3% of all Guillain-Barré syndrome cases and is characterized by axonal rather than demyelinating neuropathy. We present a pharyngeal-cervical-brachial variant case in a 55-year-old male who presented to the neurological emergency department with a three-day history of progressive and continuous dysarthria, dysphagia to solids, and tongue numbness, later developing paresthesia and weakness in the upper limbs. On physical examination, slight bilateral facial weakness, limited soft palate elevation, absent gag reflex, and limited tongue lateralization were found. Additionally, weakness was found bilaterally in the upper limbs and the flexor and extensor muscles of the neck with preserved muscle strength in the lower limbs. The patient presented upper limb hyporeflexia with lower limb hyperreflexia. A lumbar puncture was performed, revealing protein levels of 35 mg/dL and no cells in the cerebrospinal fluid. Nerve conduction studies reported acute motor and sensory axonal neuropathy (AMSAN). Management of the patient consisted of IgG administration and nasogastric tube insertion.

Anti-N-methyl-D-aspartate (NMDA) receptor encephalitis is a potentially lethal clinical entity that belongs to the group of antibody-mediated encephalitis against synaptic proteins. It shows IgG antibodies against the NR1 subunit of the NMDA receptor (NMDA-R), which have been associated with psychiatric and neurological symptoms that develop in stages in the course of the disease. The predominance of neuropsychiatric symptoms in the early stages of the disease results in an increased number of patients that search for psychiatric evaluation as their first contact with the health system. For this reason, it is vital for physicians to recognize this entity as an important differential diagnosis in their clinical practice because, despite the severity of this condition, more than 75 % of patients achieve a substantial recovery with appropriate and timely treatment. We present a review of the literature on this disease, with special emphasis on the neuropsychiatric aspects. La encefalitis por anticuerpos contra el receptor anti-N-metil-D-aspartato (NMDA) es una entidad clínica potencialmente letal perteneciente al grupo de las encefalitis mediadas por anticuerpos contra proteínas sinápticas. En esta se demuestran anticuerpos IgG contra el receptor de NMDA (NMDAr), asociados con síntomas psiquiátricos y neurológicos que se desarrollan por estadios en el curso de la enfermedad. El predominio de síntomas neuropsiquiátricos en las etapas tempranas provoca que un elevado porcentaje de pacientes busquen evaluación psiquiátrica como un primer contacto con el sistema de salud. Por esta razón, es vital que los médicos reconozcan esta entidad como un diagnóstico diferencial importante en la práctica clínica, puesto que, a pesar de la gravedad de esta condición, más de 75 % de los pacientes logra una recuperación sustancial con un tratamiento adecuado y oportuno. Presentamos una revisión de la literatura sobre esta enfermedad, con especial énfasis en los aspectos neuropsiquiátricos.

Background: During the COVID-19 pandemic, an increase in the number of Guillain-Barre syndrome (GBS) cases has been reported. Objective: To describe the clinical characteristics and prognosis of patients with GBS before and during the COVID-19 pandemic. Material and methods: Prospective cohort of GBS patients divided in two subgroups: before (2018-2019) and during (2020-2021) the COVID-19 pandemic. Clinical and paraclinical characteristics, as well as deaths, were recorded. A good prognosis was defined as independent ambulation recovery at three months. Results: Two-hundred and one patients were included (123 during and 78 before the pandemic), out of whom 69 % were males; age was 45 ± 16 years, and there was 2.5 % of in-hospital deaths. During the pandemic, a higher frequency of the demyelinating variant (50 %), bulbar cranial nerves involvement (44 % vs. 28 %), prior history of vaccination (16 % vs. 0 %), and a lower MRC score (30 ± 16.7 vs. 34.3 ± 17.7) were documented. An increase in the number of cases was observed from July to September (38 vs. 13). There were no significant differences in independent ambulation recovery or in the number of deaths. Conclusions: During the COVID-19 pandemic, a higher number of GBS cases were treated, out of which 16 % were associated with the SARS-CoV-2 vaccine; patients treated during the pandemic did not have a worse prognosis.

Background: Half of Guillain-Barre syndrome (GBS) present elevated cerebrospinal fluid (CSF) protein levels within 1 week since symptom onset and 80% within 2 weeks. Our objective was to determine the clinical and prognostic implication of albuminocytological dissociation in early GBS. Methods: An ambispective cohort study was conducted. Good outcome was considered if the patient was able to walk unaided (Guillain-Barre disability score [GDS] <= 2 points) at 3-month follow-up. Patients were classified into two groups: with and without albuminocytological dissociation; we compared clinical and paraclinic characteristics between the groups. We analyzed clinical and electrophysiological factors related to presenting early dissociation through a multivariate model. Results: We included 240 patients who fulfilled Asbury criteria for GBS. On further selection, only 94 patients fulfilled inclusion. Mean age was 45.94 +/- 17.1 years and 67% were male. Median time from symptom onset to admission was 5 days (IQR 3-6). Regarding albuminocytological dissociation and electrophysiological variants, we found a significant difference: acute inflammatory demyelinating polyneuropathy (AIDP) [60.6% vs 26.2%, p = 0.002], acute motor axonal neuropathy (AMAN) [21.2% vs 49.1%, p = 0.009] and acute motor sensory axonal neuropathy (AMSAN) [12.1% vs 1.6%, p = 0.05]. We did not observe significant differences in recovery of independent walking in short term between both groups. The presence of conduction block in any variant (OR 3.21, 95% CI 1.12-9.16, p = 0.02) and absence of sural registration (OR 5.69, 95% CI 1.48-21.83, p = 0.011) were independent factors related to early dissociation. Conclusions: Early dissociation (<7 days) is not associated with any particular clinical feature or unfavorable outcome. It is more common to see in AIDP rather than axonal variants.