35 yo woman with short history of urticarial vasculitis

Abstract: 35 yo woman with three day history of an atypical urticarial eruption

HPI: This 35 yo woman developed an urticarial eruption 8 - 10 days after starting amoxicillin for a dental infection.  At first the lesions blanched with pressure but over the last few days before her office visit the some of the lesions looked hemorrhagic.  She had mild arthralgias but no fever or malaise.

O/E: There was a wide-spread eruption mostly on legs and arms.  On her thighs the lesions appeared hemorrhagic.  The torso, head and neck were mostly spared.

Clinical Photos:

Pathology:  Two 4 mm punch biopsies were obtained from the thighs.  There was a superficial and mid dermal mixed inflammatory infiltrate composed mostly of neutrophils and eosinophils with a few lymphocytes.  The pathology was read as leucocytoclastic vasculitis vs. urticarial vasculitis.
Photomicrographs are 10x, 20x, 40x and courtesy of Dr. Jag Bhawan

Lab:  CBC nl; Chem panel nl; UA nl

Diagnosis:  Most consistent with Drug-Induced Urticarial Vasculitis (UV).

Discussion:  While UV is recognized to present as a cutaneous drug eruption, MEDLINE has no reports of UV from amoxicillin.  In this otherwise healthy woman, this seems to be the best diagnosis.  She was treated with prednisone 20 mg b.i.d. and at one week her skin lesions had completely resolved.  The dose was dropped to 20 mg per day for the second week and then she will stop.  We are aware of cases of presumably drug-induced UV which can last for weeks to months and be associated with hypocomplementemia and positive ANA and antihistone antibodies. Since this woman did well and her process resolved quickly more specialized tests were not done.

Questions:
I don't feel any further work-up is indicated at this point.  If she stays clear the case is probably closed.  If she continues to have UV-like lesions once prednisone is discontinued, a more in-depth work-up will be initiated.  Does anyone feel we should be more aggressive?

Reference:
1. eMedicine.com  Urticarial Vasculitis
2. There are no reports of UV from amoxicillin and only one with ampicillin but it is very vague.

Note:  I will ask the patient to add her comments.