A 39-year-old man comes to the office due to a skin rash on his lower extremities. Two weeks ago, he had a sore throat and was prescribed a 10-day course of amoxicillin, which he completed. His sore throat resolved, but he developed a nonpruritic rash on his legs 4 days ago. The patient reports no joint pain, abdominal pain, diarrhea, or urinary symptoms. Medical history is unremarkable, and he takes no other medications. He smokes a pack of cigarettes a day, drinks 4-6 beers on weekends, and does not use illicit drugs. The patient has had several sexual partners in his lifetime and uses condoms inconsistently.
Temperature is 36.7 C (98 F), blood pressure is 110/80 mm Hg, pulse is 80/min, and respirations are 12/min. A 0.5-cm mobile and nontender lymph node is palpable in the submandibular area. There is no pharyngeal erythema. Skin examination reveals a palpable and nonblanching rash, as shown in the exhibit.
Laboratory results are as follows:
Which of the following is the most likely cause of this patient's skin rash?

Question

A 39-year-old man comes to the office due to a skin rash on his lower extremities.  Two weeks ago, he had a sore throat and was prescribed a 10-day course of amoxicillin, which he completed.  His sore throat resolved, but he developed a nonpruritic rash on his legs 4 days ago.  The patient reports no joint pain, abdominal pain, diarrhea, or urinary symptoms.  Medical history is unremarkable, and he takes no other medications.  He smokes a pack of cigarettes a day, drinks 4-6 beers on weekends, and does not use illicit drugs.  The patient has had several sexual partners in his lifetime and uses condoms inconsistently.
Temperature is 36.7 C (98 F), blood pressure is 110/80 mm Hg, pulse is 80/min, and respirations are 12/min.  A 0.5-cm mobile and nontender lymph node is palpable in the submandibular area.  There is no pharyngeal erythema.  Skin examination reveals a palpable and nonblanching rash, as shown in the exhibit.
Laboratory results are as follows:
 Which of the following is the most likely cause of this patient's skin rash?

Quizplus · Accepted Answer

This patient developed palpable purpura toward the end of a 10-day course of amoxicillin, raising strong suspicion for medication-induced cutaneous small vessel vasculitis (CSVV). CSVV is a skin-isolated leukocytoclastic vasculitis that can be caused by drug exposure (eg, penicillin, cephalosporin, sulfonamides, phenytoin, nonsteroidal anti-inflammatory drugs, allopurinol), infection (eg, hepatitis B or C, HIV), or unknown causes. Patients usually present 7-10 days after drug (or infection) exposure with palpable purpura and/or petechiae. Visceral organ involvement (eg, kidney, lung, heart) is not a feature of CSVV and suggests a systemic vasculitides (eg, microscopic polyarteritis, granulomatosis with polyangiitis). Laboratory findings may show low serum complement levels and elevated erythrocyte sedimentation rate. Additional workup should include urinalysis (to rule out renal involvement), stool guaiac studies, and serologic studies (eg, antinuclear antibody, antineutrophil cytoplasmic antibody, cryoglobulins). Skin biopsy is not required for diagnosis but is generally recommended as the presence of leukocytoclastic vasculitis is highly suggestive of the disorder. Treatment of medication-induced CSVV primarily involves drug discontinuation and supportive care; most patients improve within days or weeks of drug cessation. Those with suspected infectious etiologies should have the underlying infection treated. (Choice A) Acute HIV infection is frequently associated with a macular or maculopapular rash on the thorax, collar region, and face. Patients also often have fever, sore throat, myalgias, headache, and nontender lymphadenopathy. Palpable purpura is not a feature of acute HIV. (Choice C) Henoch-Schönlein purpura (HSP) can cause palpable purpura, but patients also usually have arthritis/arthralgia, abdominal pain, and renal disease (hematuria). Most cases occur in those age <20. Both HSP and CSVV are associated with leukocytoclastic vasculitis, but HSP is due to IgA while CSVV is due to IgG or IgM. (Choice D) Infectious mononucleosis (IM) usually causes fever, pharyngitis/tonsillitis, fatigue, lymphadenopathy, and splenomegaly. Rash can occur after antibiotic (eg, amoxicillin, ampicillin, levofloxacin) administration but is usually maculopapular and generalized (not petechial). Although this patient had a sore throat, he has no other findings consistent with IM (a single, small, cervical lymph node is not consistent with the lymphadenopathy seen in IM). Given the presence of palpable purpura alone after recent antibiotic use, CSVV is the most likely diagnosis. (Choice E) Acute rheumatic fever occurs 2-4 weeks after group A streptococcus pharyngitis and is typically associated with migratory arthritis, carditis, erythema marginatum (evanescent, pink rash of the trunk and limbs), chorea, and/or subcutaneous nodules. Rheumatic fever is less common in adults and is not typically associated with palpable purpura. Educational objective: Cutaneous small vessel vasculitis is a skin-isolated leukocytoclastic vasculitis that usually occurs 7-10 days after drug exposure (eg, penicillin) or infection (eg, hepatitis B or C, HIV). Common findings include palpable purpura and a petechial rash. Systemic organ involvement should prompt evaluation for an alternate diagnosis. Spontaneous resolution typically occurs within days or weeks after the offending drug is discontinued (or the infection is treated). __________ References: Palpable purpura: an algorithmic approach. (http://www.ncbi.nlm.nih.gov/pubmed/7572558) Cutaneous and systemic manifestations of drug-induced vasculitis. (http://www.ncbi.nlm.nih.gov/pubmed/11816242)

A 39-Year-Old Man Comes to the Office Due to a Skin