Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (605 page)

   Serious complications may develop due to the effect of exotoxin on other organ systems, usually myocarditis or neuropathy.

   Myocarditis, usually presenting in the 2nd week of infection, may be asymptomatic, but conduction defects and arrhythmias may be serious.

   Neuropathy may present as an early or late complication of infection. Cranial nerve palsy and local neuropathy are common early complications, whereas ocular palsy and limb or diaphragmatic paralysis are late complications.

   Laboratory Findings

   Culture: Provides the definitive diagnosis of acute diphtheria. For respiratory diphtheria, collect swabs from the nasopharynx and throat, including the edges of the pseudomembrane. Alert the laboratory prior to submitting specimens to ensure that appropriate media are available. Specimens are planted on selective–differential media, like modified Tinsdale and Löeffler media, in addition to routine culture medium.
Corynebacterium diphtheriae
isolates must be tested for exotoxin production using the modified Elek immunodiffusion method. Culture from involved area is positive within 12 hours on Löeffler medium (more slowly on blood agar) (toxin-producing strain). Nasopharyngeal cultures should always be obtained when diphtheria is suspected.
If there has been prior antibiotic therapy, culture may be negative or take several days to grow.
Note:
Corynebacterium ulcerans
may cause diphtheria.

   Nucleic acid amplification: Tests have been developed both for detection/ identification of
C. diphtheriae
as well as the gene responsible for exotoxin production.

   Core laboratory: Troponin and other cardiac markers may be used to identify asymptomatic cardiac disease or assess prognosis in patients with overt myocarditis. Decreased serum glucose may be seen. Albumin and casts are frequently present in urine; blood is rarely found.

   Hematology: WBC may be moderately increased (≤15,000/μL). Moderate anemia is common.

   Serology (EIA): Not useful for diagnosis of acute infection but may be used for epidemiologic studies. Diphtheria antibody testing may also be used to assess immune function by comparing pre- and postvaccination sera.

Suggested Readings

http://wwwnc.cdc.gov/travel/yellowbook/2010/Chapter-2/diphtheria.aspx
.

Bisno AL. Acute pharyngitis.
N Engl J Med.
2001;344:205–211.

Coyle MB, Lipsky BA. Coryneform bacteria in infectious diseases: clinical and laboratory aspects.
Clin Microbiol Rev.
1990;3:227–246.

Kneen R, Dung NM, Hoa NTT, et al. Clinical features and predictors of diphtheritic cardiomyopathy in Vietnamese children.
Clin Infect Dis.
2004;39:1591–1598.

NONINFECTIOUS RESPIRATORY DISORDERS

ALLERGIC RHINITIS

   Definition

Rhinitis can be defined as symptoms of nasal irritation, sneezing, rhinorrhea, and nasal blockage lasting for at least 1 hour a day on most days. It occurs mostly in patients aged 15–25 years.

Allergic rhinitis (AR), one of the rhinitis syndromes, is a chronic inflammatory disease of the upper airways and can be seasonal or perennial. In allergic rhinitis, there is usually a clear relationship with exposure to known allergens—most frequently to pollens in seasonal rhinitis and house dust mites or household pets in perennial rhinitis. In general, allergic rhinitis can result in either inflammatory or noninflammatory causes. Many patients with allergic rhinitis have a nonallergic contribution (mixed rhinitis). Underlying causes of nonallergic rhinitis include vasomotor rhinitis, rhinitis medicamentosa, nonallergic rhinitis with nasal eosinophilia syndrome, and miscellaneous other disorders.