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Colloquially called a ‘zombie patch’, granular parakeratosis is a benign skin disease involving keratinization. It is characterized by hyperkeratotic, hyperpigmented, erythematous papules, which may coalesce into plaques. The skin plaques associated with the disease are usually found in the cutaneous folds of the body, most often the armpits.
In many people, the lesions are associated with itching. Other areas where the rash may appear include the groin, lower back, gluteal folds and the inframammary folds of skin
The typical presentation is that of a history of an axillary or intertriginous rash (a rash in an area where two areas of skin touch or rub together) rash, immediately preceded by the application of a deodorant or antiperspirant to the skin in question.
The rash is conical in shape, may be unilateral, and may appear to be confluent, with many separate lesions flowing together, or arranged in a reticulated (net-like) manner. Despite the ambiguity surrounding its etiology, granular parakeratosis is known to be a fairly uncommon condition, which shows no racial predilection, and is mostly reported to occur in women in the fourth and fifth decades of life.
There have been studies that suggest that the pathogenetic mechanisms which underlie the development of granular parakeratosis entail the defective conversion of profilaggrin to filaggrin. Filaggrin is a protein that primarily binds to keratin fibers inside epithelial cells.
It is crucial in maintaining the integrity of the barrier function of the skin. Allergic contact or irritant reactions have also been implicated as potential factors in the pathogenesis of the disease, especially when excessive amounts of topical agents have been applied to the body. Furthermore, these studies indicate that increased sweating, compounded with local irritation and an occlusive environment, may be factors to take into consideration in the mechanism of skin irritation.
However, these studies have been unable to clarify the pathogenesis of the disease in patients who did not use agents that would normally have been expected to cause irritation, occlusion or allergy. Thus, the primary mechanisms of causation of granular parakeratosis remain somewhat uncertain.
Some workers have proposed that the condition may be linked to obesity, while others indicate there may be a congenital predisposition. In addition to these, research is going on to explore whether granular parakeratosis is even a disease in itself or just a reactive process.
Granular parakeratosis is usually treated solely for aesthetic purposes, because it is a benign condition. Treatment usually involves the use of topical corticosteroids and retinoids, which are useful chiefly to reduce itching if present. However, there is no documented optimal therapy for the condition.
Other therapies used include oral antibiotics, topical vitamin D analogues and botulinum toxin injections. There have been studies that show success with the use of antifungals in the treatment of granular parakeratosis. Surgical intervention with cryotherapy has also been reported.
In addition to these therapies, patients may also take precautionary measures such as eliminating the causative agent, if allergic contact or irritant dermatitis is suspected. Similarly, these individuals would be wise to refrain from vigorous and/ or excessive washing of the intertriginous areas of the body.