60 yo F with melanoma and dusky skin


  • Identify a rare cause of hypoxia

Click here for a interactive 5 min version of the case on the Human Diagnosis Project.


60 yo woman with metastatic melanoma presents with new onset shortness of breath over the past month. She had previously been on nivolumab for her melanoma, which was complicated on severe immune-mediated enteritis. She was started on high dose steroids, infliximab and dapsone for PJP prophylaxis one month prior to presentation. Her shortness of breath has been slowly progressive and she was noted to have low oxygen saturations in the low 90s on several clinic visits. On the day of presentation, she noted some blue discoloration around her lips and finger-tips. She also reports worsening headaches, light-headedness and fatigue. She has no other medical history and takes no other medications. She is a nonsmoker.

On presentation, she is afebrile, RR in the low 20s, SaO2 84% on room air. On 8 L/min NC, her SaO2 was up to 90%. Her exam was notable for dusky skin and mucus membranes.

  • BUN 24, Cr 0.4
  • WBC – 18, Hgb 8.9, hct 27% (hct 37% 2 weeks ago), plt 264
  • ABG – pH 7.43/34/87/25  on room air

How would you interpret her ABG and pulse oximetry? 

What is your differential for this finding? 

How would you diagnose this? 

What is the most likely cause of her diagnosis? 

How would you manage this patient? 

How would you further work-up her anemia? 

What is the likely cause of her anemia? 



  1. Barclay JA, et al. Dapson-Induced Methemoglobinemia: a Primer for Clinicians. The Annals of Pharmacotherapy. 2011; 45:1130-1015.
  2. Costanzo LS. Respiratory Physiology. In: Costanzo, LS (ed). Physiology. Philadelphia, PA: Saunders Elsevier; 2018: 189-243.
  3. Benz, Jr EJ & Ebert BL. Hemoglobin Variants Associated with Hemolytic Anemia, Altered Oxygen Affinity, and Methemoglobinemias. In: Hoffman, R et al (eds). Hematology:Basic Principles and Practice. Philadelphia, PA: Elsevier; 2018: 608-615.