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A 3-year-old boy is brought to the pediatrician by his parents, who have noted excessive bleeding around the knees and elbows.


The parents have noted that the toddler bleeds very easily when the skin is scratched. Family history is significant for the presence of hemophilia in the mother’s family.



PHYSICAL EXAMINATION



VS: T 37.2°C, P 60/min, R 20/min, BP 95/70 mm Hg, 45% for height and 50% weight on the growth charts

PE: Erythema is present particularly around the knees and elbows. Purpura is noted on the elbows.


LABORATORY STUDIES



Complete blood cell count:
• Hemoglobin: 10.9 g/dL (normal: 13.4-17.4 g/dL)

• Hematocrit: 32% (normal: 40%-54%)

• Platelets: 200,000/mm3 (normal: 150,000-400,000/mm3)

Coagulation Studies
• Platelets: 412 (normal: 150-440)

• Prothrombin time: 12.5 sec (normal: 11-15 sec)

• APTT (activated partial thromboplastin time): 42 sec (normal: 26.4-35 sec)

• Bleeding time: 6 min (normal: 2-8 min)

Factor VIII: C level: 5% (normal: 25%-100%)

von Willebrand factor antigen: 145% (normal: 71%-210%)


DIAGNOSIS


Hemophilia A



PATHOPHYSIOLOGY OF KEY SYMPTOMS


The patient’s major symptoms are tied to a deficiency in the clotting process. Clot formation is a complex process, involving numerous plasma protein clotting factors, platelets, and red blood cells.


The clotting cascade results in the formation of a fibrin mesh that can trap platelets and red blood cells to form a blood clot. The 16 different blood clotting factors participate in either an extrinsic pathway and/or an intrinsic pathway. The extrinsic pathway requires an external stimulus, such as contact of the blood with the damaged portion of the vascular endothelial or blood contact with thromboplastin in the tissue spaces. The intrinsic pathway can be activated by vascular stasis, trauma to the blood, or contact with collagen. The ability to clot normally causes the loss of red blood cells from the circulation into both tissue spaces, joints, and the gastrointestinal tract.


Hemophilia A results from a hereditary deficiency in clotting factor VIII. The inheritance pattern is characterized as X-linked recessive, which means the disease is clinically significant in males but females can be carriers. Females, however, can exhibit the disease if they are the offspring of a hemophiliac father and a carrier mother.


Factor VIII is a key component in the intrinsic clotting pathway. In its absence, the clotting cascade is impaired. The coagulation panel confirms this, as the factor VIII:C level is abnormally low. The normal circulating levels of von Willebrand factor antigen rule out another common congenital bleeding disorder, von Willebrand’s disease (Fig. 26-1).


image

FIGURE 26–1 Intrinsic pathway for initiating blood clotting.

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 26

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