The clinical appearance of cutaneous pseudolymphoma is variable, ranging from discrete nodules or papules to even confluent erythroderma in certain cases.2 The high clinical variability further complicates diagnosis. Although our patient presented with 9 individual nodular lesions, this finding alone is not sufficient to have high suspicion for cutaneous pseudolymphoma without including a much broader differential diagnosis. In our case, the differential diagnosis also included cutaneous lymphoma, arthropod bite reaction, lymphomatoid papulosis, tumid lupus, follicular mucinosis, lymphocytic infiltrate of Jessner, and leukemia cutis.
The primary concern regarding diagnosis of cutaneous pseudolymphoma is the clinician’s ability to effectively differentiate this entity from a true malignant lymphoma. Immunostaining has some value by identification of heterogeneous cell–type populations with a mixed T-cell and B-cell infiltrate that is more characteristic of a benign reactive process. Subsequent polymerase chain reaction analysis can detect the presence or absence of monoclonal T-cell receptor gene rearrangement or immunoglobulin heavy chain rearrangement.3 If these monoclonal rearrangements are absent, a benign diagnosis is favored; however, these rearrangements also have been shown to exist in a case of cutaneous pseudolymphoma that earned the final diagnosis when removal of the offending agent led to spontaneous lesion regression, similar to our case.4
Many different entities have been described as causative factors for the development of cutaneous pseudolymphoma. Of those that have been considered causative, simple categories have emerged, including endogenous, exogenous, and iatrogenic causes. One potential endogenous etiology of cutaneous pseudolymphoma is IgG4-related disease.5 A multitude of exogenous causes have been reported, including several cases of cutaneous pseudolymphoma developing in a prior tattoo site.6 Viruses, specifically molluscum contagiosum, also have been implicated as exogenous causes, and a report of cutaneous pseudolymphoma development at a prior site of herpes zoster lesions has been described.7 Development of cutaneous pseudolymphoma in vaccination sites also has been reported,8 as well as more obscure inciting events such as Leishmania donovani infection and medicinal leech therapy.9
A considerable number of reported cases of cutaneous pseudolymphoma have been attributed to drugs, including monoclonal antibodies,10 herbal supplements,11 and a multitude of other medications.1 As a class, anticonvulsants are considered more likely to cause lymph node pseudolymphomas than strictly cutaneous pseudolymphomas12; however, many drugs in this class of medications have been described in the development of cutaneous pseudolymphoma.3 A review of the literature by Ploysangam et al1 revealed reports of the development of cutaneous pseudolymphomas after administration of phenytoin, carbamazepine, mephenytoin, trimethadione, phenobarbital, primidone, butabarbital, methsuximide, phensuximide, and valproic acid.
Our patient represents a rare case of strictly cutaneous pseudolymphoma caused by administration of lamotrigine. Our case demonstrated a clear temporal relation between the cessation of lamotrigine and rapid and spontaneous disappearance of cutaneous lesions. We found another case of pseudolymphoma in which lamotrigine was deemed causative, but only lymph node involvement was observed.12
Proper diagnosis of cutaneous pseudolymphoma is important not only with regard to the initial differentiation from true malignant lymphoma but in allowing for appropriate follow-up and vigilant surveillance. Cases of progression from cutaneous pseudolymphoma to true lymphoma have been reported.1,2 It is recommended that watchful follow-up for these patients be carried out until at least 5 years after the diagnosis of cutaneous pseudolymphoma is made to rule out the possibility of malignant transformation, particularly in idiopathic cases.13