What is the primary diagnosis for an idiopathic cell-mediated immune response that presents with purple, polygonal, planar, pruritic papules?

The primary diagnosis is lichen planus, which is characterized by a specific clinical presentation of pruritic, polygonal, planar papules that often have a characteristic purple color. This condition is an idiopathic inflammatory disorder primarily affecting the skin and mucous membranes. The papules are typically flat-topped and can often appear on flexural surfaces, such as the wrists or ankles, and may also present in the oral cavity as white reticular lesions.

Lichen planus is associated with a cell-mediated immune response, where T lymphocytes infiltrate the skin, leading to the distinctive lesions. The exact cause of this immune response remains unknown, but factors such as viral infections or certain medications have been implicated in triggering the condition.

In contrast, pityriasis rosea typically presents with a herald patch followed by a Christmas tree pattern of secondary lesions, and it is believed to have a viral etiology rather than being an idiopathic immune response. Tinea versicolor is a fungal infection causing hypopigmented or hyperpigmented macules and patches on the skin, which does not resemble the lesions of lichen planus. Psoriasis is characterized by well-defined, erythematous plaques with silvery scales, which again differ from the appearance