Patients who experience associated angioedema should carry epinephrine. Laboratory workup is seldom of benefit in the absence of associated signs and symptoms, and that hereditary angioedema does not present with hives. Medications, especially angiotensin converting enzyme (ACE) inhibitors, are a common cause of angioedema.
Laboratory testing in patients with chronic urticaria frequently demonstrates evidence of other autoimmune diseases, especially antimicrosomal antibodies, because these patients and their families often have varying forms of autoimmunity. There is little evidence that the antimicrosomal antibodies cause hives or that thyroid treatment resolves hives. Mild eosinophilia was noted in this patient and is likely a manifestation of allergy. When considering other causes of eosinophilia, it is important to include Addison disease; collagen-vascular diseases; and parasites, such as Strongyloides , Toxocara , and Giardia . The first two causes are diagnosed via serologic testing, and affected patients commonly lack gastrointestinal symptoms.
In the age of cost-effective and responsible evidence-based practice, extensive laboratory testing for patients with urticaria is inappropriate. All testing should be prompted by localizing signs, symptoms, or suggestive history. In this case, the patient lives in a Southern state and has eosinophilia (as well as a history of travel and drinking untreated water). She relates a history of bowel symptoms, and although these have been diagnosed in the past as IBS, further questioning reveals that she has not had any further evaluation of the symptoms. Both toxocariasis and strongyloidiasis are endemic in Southeastern states, and serologic testing for antibodies is appropriate in the presence of bowel symptoms and peripheral eosinophilia.
She also has a history of travel to an area where Giardia is endemic (Colorado) and reports drinking untreated water. Examination of stool for ova and parasites can identify organisms such as Giardia, especially if the stools are liquid; however, solid stool is not suitable for ova and parasite microscopic examination. Moreover, some organisms such as Toxocara, which causes visceral larva migrans, are not found in stool. Her history of pet ownership may be relevant if she tests positive for Toxocara. These tests were performed and were negative.
Giardia lamblia is the most common pathogenic gastrointestinal parasite worldwide and is endemic in many parts of the United States. Asymptomatic excretion is common, and a lack of history of liquid stools does not rule out the possibility of infection. Direct microscopy of fecal smears from at least three stools, with formol-ether concentration and iodine staining, can achieve 97% sensitivity, but real-life experience shows that false-negative results are common. Sodium acetate-acetic acid-formalin preservation has been used to increase the yield for various intestinal protozoans, including G lamblia. Serologic testing is now available, and coproantigen detection has evolved as a new alternative. Coproantigen detection demonstrated a sensitivity of 73 out of 74 (98.6%), and a specificity of 78 out of 78 (100%) in one study compared with 8 out of 62 (13%) of persons who were diagnosed with microscopy in the same study. Serology was less accurate in this study. IgG response to G lamblia had a sensitivity of 4 out of 7 and a specificity of 24 out of 50 (48%), and IgM response had a sensitivity of 3 out of 6 and a specificity 27 out of 48 (56%) in this study. Western blot had a sensitivity of 5 out of 7 and a specificity of 38 out of 49 (78%).
The patient's history of recurrent oral herpes simplex infection and recent use of both a sulfa drug and an nonsteroidal anti-inflammatory drug could raise the possibility of erythema multiforme, but erythema multiforme lesions are fixed and develop central necrosis, unlike the evanescent migratory lesions this patient experiences. Because her review of systems is otherwise negative for sinus, dental, respiratory, joint, or other symptoms, radiography and extensive blood testing beyond the complete blood cell count and testing for parasites are unwarranted. Her primary care physician prescribed a betamethasone-clotrimazole cream, which is not beneficial in urticaria and should rarely be prescribed for any rash, as it commonly converts simple tinea into deeply invasive Majocchi granuloma.
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