Background
Linear porokeratosis is a rare subtype of porokeratosis, a group of keratinization disorders. All porokeratosis disorders share the histopathological feature of a coronoid lamella, seen as columns of parakeratosis and dyskeratotic cells found in the granular layer of the epidermis. Linear porokeratosis presents in childhood with hyperkeratotic plaques, typically arranged in a unilateral linear formation that follow a Blaschko line distribution or dermatomes. Current therapies are reported to have unsatisfactory outcomes. Topical cholesterol 2%/ lovastatin 2% cream has been proven to be effective in some forms of porokeratosis, but has limited studies in the linear form. 

Case Presentation
A 61-year-old male presented to his family physician with erythematous plaques on the bilateral upper extremity of over 50 years duration. He has tried and failed standard treatment, including clobetasol, calcipotriene cream and diclofenac gel. Clinical presentation and pathologic examination of a skin biopsy revealing a coronoid lamellae were consistent with bilateral linear porokeratosis. Through a PubMed search, there have been limited reported cases of unilateral linear porokeratosis, but there have not been any reported cases of bilateral linear porokeratosis.

Discussion
A current theory for development is a two-hit mutation in the phosphomevalonate kinase (PVMK) and mevalonate diphosphate decarboxylase (MVD) genes of the cholesterol synthesis pathway, causing loss of function of the genes. These mutated genes inhibit the cholesterol synthesis pathway. Because cholesterol is an essential factor in the overall health of the stratum corneum, cholesterol depletion causes premature apoptosis of the keratinocytes, leading to the formation of the porokeratosis. 
The compounded cholesterol 2%/lovastatin 2% ointment provided a profound decrease in the hyperkeratotic scaling and erythema associated with our patient’s bilateral linear porokeratosis. After a 12 week trial, the overall size of the patches and plaques were significantly reduced in the treated areas. The mechanism of action of the targeted therapy and the results our patient achieved support the two-hit mutation theory (loss of function mutations in PVMK and MVD) in causing of linear porokeratosis. Cholesterol and lovastatin have an established safety profile and offers a relatively inexpensive alternative treatment option that may have better outcomes than current standard therapies. 


Darlene Diep

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