Doctors reported an unusual case of a 56-year-old man who developed a serious blood disorder after a respiratory infection caused by Mycoplasma pneumoniae bacteria. His condition was complicated because he also had pernicious anemia, a separate blood problem related to vitamin B12 deficiency. The patient’s immune system mistakenly attacked his red blood cells, especially in cold temperatures. After receiving vitamin B12 injections and antibiotics for two weeks, his blood counts improved significantly within a month. This case shows how infections can trigger unexpected immune reactions and highlights why doctors need to consider multiple conditions when diagnosing blood disorders.

The Quick Take

  • What they studied: How a common lung infection (Mycoplasma pneumoniae) triggered a rare immune condition that destroyed red blood cells in a patient who also had vitamin B12 deficiency anemia
  • Who participated: One 56-year-old man who came to the hospital with a persistent cough and pale skin
  • Key finding: The patient had two separate blood problems happening at the same time: his immune system was attacking his red blood cells (triggered by the lung infection), and he had low vitamin B12 levels. Both conditions improved with antibiotics and vitamin B12 injections within four weeks
  • What it means for you: This case suggests that doctors should check for multiple blood problems when patients have unusual symptoms, especially after infections. However, this is a very rare situation, so most people with respiratory infections won’t develop this condition

The Research Details

This is a case report, which means doctors documented one patient’s medical story in detail. The patient came to the hospital with a ten-day cough and noticed his skin looked pale. Doctors ran blood tests and discovered his red blood cells were being destroyed by his own immune system. They also found he had very low vitamin B12 levels and antibodies (immune proteins) attacking his stomach cells, which is why his body couldn’t absorb B12 properly. Tests confirmed he had a Mycoplasma pneumoniae infection, a type of bacteria that causes atypical pneumonia. The doctors treated him with vitamin B12 injections and an antibiotic called doxycycline for two weeks, then tracked how his blood improved over the next month.

Case reports are important because they describe unusual or rare situations that doctors might not see often. By documenting this patient’s experience in detail, other doctors can learn to recognize similar patterns and diagnose patients faster. This case is particularly valuable because it shows how an infection can trigger an immune reaction that affects blood cells, and how this can happen alongside another blood disorder

This is a single case report, which means it describes one patient’s experience rather than studying many people. While case reports are useful for identifying rare conditions, they cannot prove that the infection always causes this blood problem in other patients. The diagnosis was confirmed with multiple tests (blood work, antibody tests, and bacterial identification), which makes the findings more reliable. However, because only one patient was studied, we cannot know how common this combination of conditions is or how often it occurs

What the Results Show

The patient presented with a cough and pale skin caused by two simultaneous blood problems. First, his immune system was producing special proteins called cryoagglutinins that attacked his red blood cells, especially in cold temperatures. Second, he had pernicious anemia, meaning his stomach couldn’t absorb vitamin B12 from food because his immune system was attacking the cells that help with absorption. Blood tests showed his red blood cells were being destroyed (hemolysis), and he had very low vitamin B12 levels. The Mycoplasma pneumoniae infection was confirmed through antibody testing. After treatment with vitamin B12 injections and doxycycline antibiotics for 14 days, his hemoglobin levels (a measure of red blood cells) improved significantly within four weeks, and his other blood markers returned toward normal.

The patient’s blood tests showed megaloblastic anemia, which means his red blood cells were abnormally large due to B12 deficiency. The direct Coombs test was positive for complement C3d, indicating his immune system was actively destroying red blood cells. The presence of both cryoagglutinins (cold-activated antibodies) and intrinsic factor antibodies (which block B12 absorption) in the same patient was particularly unusual and complicated his diagnosis

Mycoplasma pneumoniae infections are known to sometimes trigger immune reactions that attack red blood cells, but this usually happens without the additional complication of pernicious anemia. Having both conditions at the same time is extremely rare. The case demonstrates that doctors should consider multiple diagnoses when patients have unusual blood test results, especially after infections. Previous research has shown that atypical infections can trigger autoimmune responses, but this specific combination highlights an important diagnostic lesson

This is a single case report, so we cannot determine how often this combination of conditions occurs or whether the treatment would work the same way in other patients. We don’t know if the patient had any other health conditions that might have contributed to his illness. The report doesn’t provide long-term follow-up information beyond four weeks, so we don’t know if the improvement continued or if the patient had any relapses. Because only one patient was studied, these findings cannot be generalized to larger populations

The Bottom Line

If you have a persistent cough combined with unusual paleness, shortness of breath, or fatigue, see a doctor for blood tests. If you’re diagnosed with a respiratory infection and develop symptoms of anemia (extreme tiredness, weakness, pale skin), inform your doctor immediately. People with pernicious anemia should ensure they receive regular B12 supplementation. This case suggests doctors should consider multiple blood disorders when patients have unusual symptoms after infections, though this specific combination is very rare. Confidence level: This recommendation is based on a single case, so it should be considered as a learning point rather than a definitive treatment guideline

This case is most relevant to doctors and healthcare providers who treat patients with blood disorders or atypical infections. Patients with pernicious anemia should be aware that infections might complicate their condition. People with autoimmune conditions may find this case informative about how infections can trigger immune reactions. Most people with respiratory infections will not develop this rare complication, so general readers should not be overly concerned about catching Mycoplasma pneumoniae

In this patient, blood counts began improving within two weeks of starting treatment and showed significant improvement within four weeks. However, this timeline may vary depending on individual factors. Long-term vitamin B12 supplementation will likely be needed indefinitely for pernicious anemia

Want to Apply This Research?

  • Track hemoglobin levels and energy levels weekly if you have pernicious anemia or have recently had a respiratory infection. Record any symptoms like unusual tiredness, shortness of breath, or pale skin, and note the date and severity
  • If you have pernicious anemia, set reminders for your B12 injections or supplements. If you develop a respiratory infection, schedule follow-up blood work to ensure your blood counts remain normal. Keep a symptom diary noting any new fatigue or breathing difficulties
  • For patients with pernicious anemia, maintain regular B12 level monitoring every 3-6 months. After any respiratory infection, consider requesting a complete blood count to rule out complications. Track energy levels and symptoms consistently to catch any changes early

This case report describes one patient’s rare medical experience and should not be used for self-diagnosis. If you have symptoms of anemia (extreme fatigue, shortness of breath, pale skin) or a persistent cough, consult a healthcare provider for proper evaluation and testing. This information is educational and does not replace professional medical advice. Do not start or stop any medications without consulting your doctor. If you have pernicious anemia or autoimmune conditions, work with your healthcare team to monitor your health and adjust treatment as needed.