Headache and Methemoglobinemia

Methemoglobinemia and Delayed Encephalopathy After 5-Bromo-2-Nitropyridine Poisoning: A Rare Case Report

5-bromo-2-nitropyridine, an intermediate in the synthesis of pharmaceutical and pesticide products, is toxic to the human body. However, 5-bromo-2-nitropyridine poisoning has not been previously reported. Here, we report the case of a 40-year-old man who suffered skin and respiratory tract exposure to leaked 5-Bromo-2-nitropyridine at work. After exposure, the patient rapidly developed dizziness, fatigue, nausea, vomiting, chest distress, diffuse cyanosis, and coma. Methemoglobinemia, hemolytic anemia, rhabdomyolysis, and acute renal failure were observed after admission. He improved markedly after treatment, but delayed encephalopathy was confirmed 82 days after the exposure. This case highlights that 5-bromo-2-nitropyridine can be absorbed through the skin and respiratory tract, resulting in methemoglobinemia and delayed encephalopathy.

Two cases of methaemoglobinaemia and haemolysis due to poisoning after skin absorption of 4-chloro-1-nitrobenzene

INTRODUCTION

While 4-chloro-1-nitrobenzene has oxidising properties and can lead to methaemoglobinaemia and haemolysis, such reports are rare. We herein describe two cases of 4-chloro-1-nitrobenzene poisoning after skin exposure and detail relevant clinical characteristics and treatment outcomes.

CASE PRESENTATION

A 45-year-old man and his 32-year-old male co-worker presented at our department shortly after skin exposure to 4-chloro-1-nitrobenzene. They developed similar symptoms, including dizziness, dyspnoea, excessive fatigue, and coma. Patients' chest inspection yielded normal findings. Despite maximal oxygen supplementation, neither patient exhibited improvements in the following clinical parameters: diffuse cyanosis, chocolate-coloured blood, and decreased pulse oximetry. For patients 1 and 2, methaemoglobin levels at admission were 78.6% and 63.6%, and 4-chloro-1-nitrobenzene concentrations were 4.12 μg/mL and 2.89 μg/mL, respectively. Their symptoms and methaemoglobin levels improved after we cautiously administered methylene blue; we subsequently detected oxidative haemolysis (confirmed by peripheral blood smears) that later resolved without further aggravation. No further episodes of anaemia were documented via telephone follow-up for eight months after hospital discharge for either patient.

DISCUSSION

Typical features of methaemoglobinaemia included diffuse cyanosis, dark chocolate-coloured blood, elevated partial pressure of oxygen, and decreased pulse oximetry saturation. Haemolysis likely occurred secondary to the toxic effects of 4-chloro-1-nitrobenzene.

Acquired methemoglobinemia: A systematic review of reported cases

INTRODUCTION

Acquired methemoglobinemia may cause cyanosis and tissue ischemia unresponsive to oxygen supplementation.

METHODS

We performed a literature search to identify cases of acquired methemoglobinemia published between 1980 and 2020. Clinical, diagnostic, and treatment details were extracted from eligible cases.

RESULTS

A total of 76 reports involving 87 cases were analyzed. The median age at presentation was 32.5 with male to female ratio of 1.6. Cyanosis and SpO₂ <90 % were reported in 82 % and 60 % of cases, respectively. Dapsone or cocaine-based anesthetics were causative in 52 % of cases; most anesthetic-related cases occurred in the peri-procedural setting. Methylene blue (MB) and red cell transfusion were given in 71 % and 10 % of cases, respectively. Compared to MB untreated patients, MB treated patients were more likely to be cyanotic (91.9 % vs 54.2 %), had higher proportions (%) and levels (g/dL) of methemoglobin (MetHb) - 33.2 % vs 15.3 % and 3.1 g/dL vs 1.2 g/dL, respectively. We found that among cyanotic cases, the median MetHb level was 3.0 g/dL (0.4-12.3 g/dL) with 74 % of values ≥ 1.5 g/dL. An SaO2:SpO₂ ratio of >1 was not universally present, but always coincided with an [SaO₂-SpO₂] delta value greater than zero.

CONCLUSIONS

Cyanosis and hypoxemia were not universal findings of acquired methemoglobinemia in our series. In addition, not all patients had cyanosis at MetHb ≥ 1.5 g/dL or an SaO2:SpO₂ ratio of >1. All those with an SaO₂:SpO₂ >1 did, however, have a delta value greater than zero - a finding not previously reported which we feel holds diagnostic value.