Fig. 34.1
Upper panel reveals a middle-aged woman who presented with a 2-week history of an asymptomatic papulosquamous eruption characteristic of pityriasis rosea. Lower panel reveals a young woman with eruptive guttate psoriasis
Case
A patient presents with acute eruption of multiple scaly, reddish papules over the trunk and extremities.
The clinical differential diagnosis on most pathology requisition forms for this presentation includes any number of the following four disorders:
guttate psoriasis
pityriasis rosea (PR)
pityriasis lichenoides chronica (PLC), and
secondary syphilis.
Clinical Clues
Unlike patients with the other disorders, patients with PLC report a chronic or waxing and waning eruption, and almost never present acutely. PLC is generally asymptomatic and follows a slow and insidious course; hence, patients present months after the onset of the first crop of lesions. Examination invariably reveals lesions at various stages of development and healing (red papules followed by finely scaly, thin flat-topped papules followed by brownish or hypo-pigmented macules).
Patients with secondary syphilis may present acutely with systemic symptoms, including low-grade fever and lymphadenopathy. They may or may not have evidence of primary chancre. They usually have mucosal and palmoplantar lesions.
Patients with papular PR also present acutely, reporting a rapidly progressive eruption. They may have a persistent or fading herald patch. Even when the lesions are papules (which occurs more frequently in dark-skinned individuals), the eruption still respects the so-called Christmas-tree pattern and upon close inspection, some papules may show a collarette of fine scale.
Finally, most patients with the first episode of acute guttate psoriasis recall a recent upper respiratory infection. Guttate psoriasis lesions tend to be more intensely red than papules of PR, PLC, and secondary syphilis.
A drug eruption may occasionally be papulosquamous, especially mimicking PR.
How Helpful Is the Pathology?
Very helpful + + +
In the above clinical presentation, two or more biopsies should result in an accurate diagnosis in practically all cases. The need for more than one biopsy is due to the fact that the diagnostic findings of guttate psoriasis and PLC are present in a short phase in the evolutionary life of each lesion. The histological findings in the two disorders are so dynamic that a very early or very old lesion may miss the diagnostic findings.