A 9-year-old boy from rural Asia was brought to the clinic by his parents for complaints of being tired and “blue.” Further history reveals that he has had frequent episodes of squatting after exertion which relieves some of the symptoms temporarily. On exam, he has clubbing of the fingers and toes with cyanosis of the lips and oral mucous membranes (Figure 41-1). A harsh systolic ejection murmur is best heard at the left mid and upper sternal border. An echocardiogram confirms the diagnosis of tetralogy of Fallot.
Clubbing is the enlargement of the distal fingers or toes along with the formation of convex shaped fingernails or toenails.
Cyanosis is the bluish discoloration of the skin or mucous membranes due to increased quantity of deoxyhemoglobin in the blood. Unless otherwise specified, cyanosis in this chapter refers to central cyanosis.
The exact etiology of clubbing is unknown. However, it has been hypothesized that it may result from megakaryocytes that have bypassed the pulmonary vascular bed and entered the systemic circulation or from platelet clumps that form and/or enter the systemic circulation. They then release platelet-derived growth factor causing clubbing.1,2
A right to left cardiac shunt or significant lung disease easily allows platelets to bypass the lungs and hence cause clubbing. Conditions that result in platelet excess, that is, inflammatory bowel disease, may also result in clubbing.
Cyanosis occurs due to reduced capillary blood oxygen saturation and becomes apparent when deoxyhemoglobin in the blood exceeds a value of 3 to 5 g/dL (corresponding arterial saturations of 70 to 85 percent).3
