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Year : 2017  |  Volume : 10  |  Issue : 2  |  Page : 211-214  

Disproportionate dyspnea in a patient with pneumonia

Department of Respiratory Medicine, AJ Institute of Medical Sciences, Mangalore, Karnataka, India

Date of Web Publication14-Mar-2017

Correspondence Address:
Vishnu Sharma Moleyar
Department of Respiratory Medicine, AJ Institute of Medical Sciences, Mangalore, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0975-2870.202099

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In severe pneumonia, dyspnea occurs due to hypoxia. Usually, in pneumonia, dyspnea is proportional to the extent of lung parenchymal lesion. When a patient with pneumonia presents with disproportionate dyspnea, other causes for dyspnea should be evaluated. Here, we present a 48-year-old female with pneumonia, found to have disproportionate dyspnea. Her hypoxia did not improve despite adequate antibiotic and oxygen therapy. On further enquiry, she admitted taking dapsone for leprosy. She had saturation gap diagnostic of methemoglobinemia. Diagnosis was confirmed by estimation of methemoglobin level in blood. She was treated with intravenous methylene blue and recovered. When a patient has disproportionate dyspnea, methemoglobinemia should be considered as a differential diagnosis.

Keywords: Disproportionate dyspnea, methemoglobinemia, pneumonia, saturation gap

How to cite this article:
Moleyar VS, Bhat AC, Madhusudan Y, Harsha D S. Disproportionate dyspnea in a patient with pneumonia. Med J DY Patil Univ 2017;10:211-4

How to cite this URL:
Moleyar VS, Bhat AC, Madhusudan Y, Harsha D S. Disproportionate dyspnea in a patient with pneumonia. Med J DY Patil Univ [serial online] 2017 [cited 2020 Sep 18];10:211-4. Available from:

  Introduction Top

A 48-year-old female homemaker was admitted with history of low-grade fever, generalized body ache, and weakness for the last 7 days. She also had developed dyspnea on exertion and dry cough for 3 days. She had no upper respiratory symptoms or other respiratory or cardiac symptoms. She had no history of premorbid lung or cardiac disease; no gastrointestinal symptoms; and no diabetes, hypertension, or systemic illness.

  Question 1 Top

Which of the following is the most likely diagnosis in this patient?

  1. Atypical pneumonia
  2. Upper respiratory tract infection
  3. Cardiogenic pulmonary edema
  4. Acute exacerbation of bronchial asthma
  5. Lobar pneumonia.

  Answer A Top

Atypical pneumonia.

Atypical pneumonia usually presents with low-grade fever, dry cough followed by dyspnea. She had no upper respiratory symptoms. She had no cardiac symptoms or cardiac disease in past. Dyspnea on exertion without any of the other cardiac symptoms, nocturnal dyspnea, and orthopnea exclude the possibility of cardiogenic pulmonary edema. She had no history of bronchial asthma and had no symptoms of bronchial asthma. Lobar pneumonia usually presents with high-grade fever, sometimes with rigor and chills with cough, expectoration and pleuritic chest pain.

Physical findings

Respiratory rate was 26/min. Pulse rate was 108/min. Blood pressure was 140/80 mmHg. Oxygen saturation (SpO2) while breathing room air was 88%.

Respiratory system examination revealed a few scattered crepitations bilaterally. Other systemic examinations were normal.

  Question 2 Top

In which of the following conditions, dyspnea will be usually proportionate to physical findings?

  1. Atypical pneumonia
  2. Sepsis
  3. Lobar pneumonia
  4. Pulmonary embolism
  5. Chronic obstructive pulmonary disease.

  Answer C Top

Lobar pneumonia.

In lobar pneumonia, signs of consolidation will be evident. In all other conditions, physical findings may be minimal.

  Question 3 Top

What are the other causes of disproportionate dyspnea in pneumonia?

  Answer Top

In patients with preexisting lung disease with poor respiratory reserve, associated obstructive airway disease, pleural disease, kyphoscoliosis, pulmonary edema, heart disease, metabolic disorders leading to acidosis, severe anemia, distended abdomen, systemic illness, and hemoglobinopathies, disproportionate dyspnea may be encountered when they develop pneumonia.

Further evaluation

Arterial blood gas (ABG) analysis and chest X-ray were done. Chest X-ray was normal. After ABG, the patient was started on 4 L of oxygen.

  Question 4 Top

In which of the following conditions, chest X-ray will always be abnormal in a patient with dyspnea?

  1. Airway disease
  2. Atypical pneumonia
  3. Lobar pneumonia
  4. Early interstitial lung disease
  5. Pulmonary embolism.

In lobar pneumonia, chest X-ray will show consolidation. In all other conditions, chest X-ray may be normal at times.

Other causes for normal chest X-ray with dyspnea

  1. Cardiac causes
  2. Severe anemia
  3. Subdiaphragmatic causes
  4. Metabolic acidosis
  5. Hemoglobinopathies.

ABG was taken with 4 L supplemental oxygen.

ABG: pH - 7.51; PCO2-15.2; PO2-162.8; HCO3-12.

  Question 5 Top

What is the diagnosis from ABG?

  Answer Top

Respiratory alkalosis.

  Question 6 Top

Which of the following is least likely to cause respiratory alkalosis?

  1. Pneumonia
  2. Acute exacerbation of asthma
  3. High-grade fever
  4. Neurogenic pulmonary edema
  5. Severe kyphoscoliosis.

  Answer E Top

Severe kyphoscoliosis.

Severe kyphoscoliosis will lead to respiratory acidosis due to hypoventilation.

Other investigations

  • Hemoglobin - 10 g/dl
  • Total leukocyte count – 11,200 cells/cumm
  • Erythrocyte sedimentation rate - 75 mm/h
  • Platelet - 1.75 lakhs
  • Packed cell volume - 32%
  • Peripheral smear - mild normocytic, hypochromic anemia
  • Two-dimensional echo - normal.

Further story

The patient was treated with clarithromycin 500 mg twice daily and intravenous (IV) ceftriaxone 1 g thrice daily with oxygen 4 L. The patient improved clinically, but in spite of oxygen supplementation, 4 L SpO2 was 91%–92%. The degree of hypoxia was more than her clinical findings. PO2 in ABG was 106, not correlating with SpO2.

  Question 7 Top

What does pulse oximetry measures?

  1. Hemoglobin level in blood
  2. Amount of oxygen contained in blood
  3. Pulse rate
  4. Percentage of hemoglobin saturated with oxygen (SpO2)
  5. SpO2 and heart rate.

  Answer E Top

SpO2 and heart rate.

Normal SpO2 is 95%–99%.

  Question 8 Top

Which of the following does not interfere with pulse oximeter readings?

  1. Dark skin
  2. Nail polish
  3. Hyperbilirubinemia
  4. Dyshemoglobinemias
  5. Hypotension.

  Answer C Top


  Question 9 Top

In which of the following poisoning/conditions, saturation gap is not seen?

  1. Carbon monoxide
  2. Methemoglobinemia
  3. Cyan hemoglobin
  4. Trinitrotoluene
  5. Hydrogen sulfide.

  Answer C Top

Saturation gap means disproportion in Pulse oximetry and ABG.

On further enquiry, she admitted taking dapsone since 6 months for Hansen's disease.

  Question 10 Top

What is the most likely diagnosis with this history of dapsone intake?

  Answer Top

Dapsone-induced methemoglobinemia.

  Question 11 Top

What is the next diagnostic investigation?

  Answer Top

  • Estimation of methemoglobin levels in blood
  • Observed value in this patient was 8.5%
  • Many drugs can lead to methemoglobinemia.

  Question 12 Top

Which of the following drug is least likely to cause methemoglobinemia?

  1. Benzocaine
  2. Rifampicin
  3. Sulfonamides
  4. Compounds containing nitrates
  5. Metoclopramide.

  Answer B Top


  Question 13 Top

Which is a wrong statement regarding methemoglobinemia?

  1. Central cyanosis
  2. Cyanosis is a late feature
  3. Cyanosis may not improve with supplemental oxygen
  4. Lead to shift of oxygen dissociation curve to left
  5. PO2 may be normal in ABG.

  Answer B Top

Cyanosis is a late feature.

Co-oximetry is used to measure blood concentration of various forms of hemoglobin.

  1. Normal range of methemoglobin in blood is <2%. Methemoglobin level above 70% is lethal. Severe symptoms with tissue hypoxia will occur when the level is above 20%. The color of the blood in methemoglobinemia is chocolate brown. Treatment for methemoglobinemia is methylene blue 1–2 mg/kg IV over 15 min. Methylene blue is contraindicated in glucose-6-phosphate dehydrogenase deficiency.[6],[7]

  Question 14 Top

Which is not useful in methemoglobinemia?

  1. Exchange transfusion
  2. Hyperbaric oxygen therapy
  3. Systemic steroids
  4. IV methylene blue
  5. Hydration.

  Answer C Top

Systemic steroids.

  • Was treated with IV methylene blue
  • Made uneventful complete recovery.

Learning points

When breathlessness is out of proportion to clinical findings, atypical pneumonia, pulmonary vascular disease, other systemic causes, metabolic causes, or decreased oxygen carriage should be considered in differential diagnosis. Saturation gap is diagnostic of dyshemoglobinemias.

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Conflicts of interest

There are no conflicts of interest.

  References Top

do Nascimento TS, Pereira RO, de Mello HL, Costa J. Methemoglobinemia: From diagnosis to treatment. Rev Bras Anestesiol 2008;58:651-64.  Back to cited text no. 1
Percy MJ, McFerran NV, Lappin TR. Disorders of oxidised haemoglobin. Blood Rev 2005;19:61-8.  Back to cited text no. 2
Mansouri A, Lurie AA. Concise review: Methemoglobinemia. Am J Hematol 1993;42:7-12.  Back to cited text no. 3
Curry S. Methemoglobinemia. Ann Emerg Med 1982;11:214-21.  Back to cited text no. 4
Ward KE, McCarthy MW. Dapsone-induced methemoglobinemia. Ann Pharmacother 1998;32:549-53.  Back to cited text no. 5
Ash-Bernal R, Wise R, Wright SM. Acquired methemoglobinemia: A retrospective series of 138 cases at 2 teaching hospitals. Medicine (Baltimore) 2004;83:265-73.  Back to cited text no. 6
Wright RO, Lewander WJ, Woolf AD. Methemoglobinemia: Etiology, pharmacology, and clinical management. Ann Emerg Med 1999;34:646-56.  Back to cited text no. 7
Esbenshade AJ, Ho RH, Shintani A, Zhao Z, Smith LA, Friedman DL. Dapsone-induced methemoglobinemia: A dose-related occurrence? Cancer 2011;117:3485-92.  Back to cited text no. 8


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