Case 11

Published on 18/02/2015 by admin

Filed under Allergy and Immunology

Last modified 18/02/2015

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CASE 11

Mary is 20 months of age and has been hospitalized with a fever, irritability, and moderate dehydration. Blood work suggests a bacterial infection, with elevated neutrophils (>96%; normal: ˜70%), although the chest radiograph and urinalysis are normal. Computed tomography (CT) indicated intracranial evidence for generalized edema with some compression of the ventricles. Despite the risk associated with elevated cerebrospinal fluid (CSF) pressure, a lumbar puncture was performed that showed an elevated white cell count. An analysis of the CSF by polymerase chain reaction (PCR) assay revealed the presence of Neisseria meningitidis. Mary has been receiving intravenous antibiotics for 30 hours, and there is some improvement in her condition. Query into the child’s background indicated that Mary had been breast fed until she was 3 months of age and had been relatively healthy until this recent infection. Detailed family history reveals that a distant male cousin and an aunt both died at an early age (<2 years) of meningitis. What further tests might you order? What is the significance of the history and findings?

QUESTIONS FOR GROUP DISCUSSION

1. In several of the preceding cases, we have considered patients who presented with bacterial infections. Unlike these patients, who had recurrent infections with several gram-negative and/or gram-positive bacteria, Mary has only presented with infection with Neisseria meningitidis. Why is a phagocyte or B cell defect unlikely?

2. The family history revealed that both males and females had presented with this type of infection. What does this indicate? Explain the term autosomal recessive.

3. We have learned in previous cases that bacterial infections are often indicative of a B cell, phagocyte, or complement disorder. Explain how an overall test of complement activity using CH50 and AH50 can be used to determine if there is a problem with activation of the (a) classical pathway, (b) alternative pathway, or (c) terminal pathway of complement?

4. Explain how (a) the classical pathway of complement and (b) the alternative pathway are activated.

5. List the biologic activities of the proteolytic fragments generated from the activation of (a) the classical pathway and (b) the alternative pathway of complement.

6. How would deficiencies in the early components of the classical pathway of complement present clinically?

7. Describe the two types of meningococcal vaccines available and the (a) limitations of each and (b) advantages of each.

8. Why is a defect in the C3 component of complement so devastating?

9. Describe the role of properdin and the significance of the fact that the gene that encodes this protein is expressed on the X chromosome.

10. Describe the role of each of the following complement regulatory proteins: (a) decay accelerating factor, (b) S-protein, (c) CD59, (d) homologous restriction factor, and (e) C1 inhibitor protein.

RECOMMENDED APPROACH

Implications/Analysis of Family History

An inquiry into Mary’s family history revealed that a distant male cousin and an aunt had both died of meningitis at an early age (<2 years). An inherited disorder is suspected when genetically linked individuals present with the same type of clinical history. Autosomal recessive defects are suspected when both males and females are affected.

Implications/Analysis of Clinical History

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