Pseudoporphyria Workup

Updated: May 11, 2018
  • Author: Vineet Mishra, MD, FAAD; Chief Editor: Dirk M Elston, MD  more...
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Workup

Laboratory Studies

Of critical importance in the diagnosis of pseudoporphyria is the exclusion of true porphyria. The most important test is a serum/plasma porphyrin assay. If this result is negative, the patient does not have a true porphyria. If the serum/plasma porphyrin assay is unavailable, erythrocytes, urine, and stool may be evaluated for abnormal porphyrin levels. However, such evaluations can represent a diagnostic challenge to complete for patients who may be anuric in the setting of end stage renal disease. [73]

Other causes of photosensitivity, such as connective tissue disease, must be excluded by obtaining a serum antinuclear antibody titer and more specific studies, such as antibodies to Ro, La, ribonucleoprotein, Smith, and double-stranded DNA.

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Procedures

If the diagnosis of pseudoporphyria is suspected, biopsies for histologic evaluation with hematoxylin and eosin stains and direct immunofluorescence should be performed. Serum samples may also be obtained for indirect immunofluorescence evaluation to aid in the exclusion of bullous pemphigoid.

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Histologic Findings

The histologic features of pseudoporphyria are similar to those of porphyria cutanea tarda (PCT) with cell-free subepidermal bullae and festooning of the dermal papillae. [67] The thickness of the blood vessel wall may prove helpful in differentiating pseudoporphyria from porphyria cutanea tarda.

In a comparative histologic study from biopsy samples of patients with porphyria cutanea tarda and pseudoporphyria, Maynard and Peters found thickened blood vessel walls in 11 of 13 patients with porphyria cutanea tarda. In contrast, similar findings in only 1 of 9 patients with pseudoporphyria were present. [74]

Porphyria cutanea tarda and pseudoporphyria have similar, nonspecific direct immunofluorescence findings of granular deposits of immunoglobulins, mostly IgG, and C3 at the basement membrane zone and in the perivascular region. Although direct immunofluorescence is not a useful tool in distinguishing pseudoporphyria from porphyria cutanea tarda, it is helpful in the evaluation of other entities in the differential diagnosis of pseudoporphyria, specifically epidermolysis bullosa acquisita. Epidermolysis bullosa acquisita can be ruled out by the lack of intense, linear immunoreactants at the dermal-epidermal junction. Neither porphyria cutanea tarda nor pseudoporphyria has circulating autoantibodies detected by indirect immunofluorescence study.

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