Medical Journal of Dr. D.Y. Patil Vidyapeeth

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

Disproportionate dyspnea in a patient with pneumonia

Vishnu Sharma Moleyar, Alka C Bhat, Y Madhusudan, DS Harsha 
 Department of Respiratory Medicine, AJ Institute of Medical Sciences, Mangalore, Karnataka, India

Correspondence Address:
Vishnu Sharma Moleyar
Department of Respiratory Medicine, AJ Institute of Medical Sciences, Mangalore, Karnataka


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.

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;10:211-214

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 ];10:211-214
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Full Text


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

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

Atypical pneumoniaUpper respiratory tract infectionCardiogenic pulmonary edemaAcute exacerbation of bronchial asthmaLobar pneumonia.

 Answer A

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

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

Atypical pneumoniaSepsisLobar pneumoniaPulmonary embolismChronic obstructive pulmonary disease.

 Answer C

Lobar pneumonia.

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

 Question 3

What are the other causes of disproportionate dyspnea in pneumonia?


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

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

Airway diseaseAtypical pneumoniaLobar pneumoniaEarly interstitial lung diseasePulmonary 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

Cardiac causesSevere anemiaSubdiaphragmatic causesMetabolic acidosisHemoglobinopathies.

ABG was taken with 4 L supplemental oxygen.

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

 Question 5

What is the diagnosis from ABG?


Respiratory alkalosis.

 Question 6

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

PneumoniaAcute exacerbation of asthmaHigh-grade feverNeurogenic pulmonary edemaSevere kyphoscoliosis.

 Answer E

Severe kyphoscoliosis.

Severe kyphoscoliosis will lead to respiratory acidosis due to hypoventilation.

Other investigations

Hemoglobin - 10 g/dlTotal leukocyte count – 11,200 cells/cummErythrocyte sedimentation rate - 75 mm/hPlatelet - 1.75 lakhsPacked cell volume - 32%Peripheral smear - mild normocytic, hypochromic anemiaTwo-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

What does pulse oximetry measures?

Hemoglobin level in bloodAmount of oxygen contained in bloodPulse ratePercentage of hemoglobin saturated with oxygen (SpO2)SpO2 and heart rate.

 Answer E

SpO2 and heart rate.

Normal SpO2 is 95%–99%.

 Question 8

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

Dark skinNail polishHyperbilirubinemiaDyshemoglobinemiasHypotension.

 Answer C


 Question 9

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

Carbon monoxideMethemoglobinemiaCyan hemoglobinTrinitrotolueneHydrogen sulfide.

 Answer C

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

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


Dapsone-induced methemoglobinemia.

 Question 11

What is the next diagnostic investigation?



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

 Question 12

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

BenzocaineRifampicinSulfonamidesCompounds containing nitratesMetoclopramide.

 Answer B



 Question 13

Which is a wrong statement regarding methemoglobinemia?

Central cyanosisCyanosis is a late featureCyanosis may not improve with supplemental oxygenLead to shift of oxygen dissociation curve to leftPO2 may be normal in ABG.

 Answer B


Cyanosis is a late feature.

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

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

Which is not useful in methemoglobinemia?

Exchange transfusionHyperbaric oxygen therapySystemic steroidsIV methylene blueHydration.

 Answer C


Systemic steroids.

Was treated with IV methylene blueMade 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.


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