several pathogenetic mechanisms have been proposed in the past , but the entity still remains unclear .
first described its histopathological findings in 1999 , where the transepidermal elimination of urate - like crystals was observed .
the term  necrotizing infundibular crystalline folliculitis was first used in 2001 by kossard et al . .
in 2011 , denisjuk et al .   proposed to rename the lesion to  necrotizing ostial crystalline folliculitis due to the fact that in their study the most important pathognomonic feature of urate - like crystals was their location in the ostia and rarely in the infundibular region of the hair follicles .
microscopically , a follicular invagination is observed , filled with cellular debris and keratin lamellae embedded in alcian blue - positive filamentous mucinous material   which resembles urate - like crystalline material .
here we describe the case of a 71-year - old male patient who presented with multiple hyperkeratotic lesions of the forehead ( fig .
biopsy material obtained from the patient was fixed in formalin , embedded in paraffin , cut at 5 m and stained with hematoxylin - eosin , periodic acid - schiff and alcian blue according to standard procedures .
on histological examination , a follicular invagination containing some cellular debris and keratin lamellae was observed ( fig .
2a , b ) . in the ostium of this follicular structure , filamentous mucinous material
numerous fungal elements consistent with malassezia yeasts were seen ( data not shown ) , but no bacteria were observed .
the clinical and histological aspect of our case is quite typical for the so - called  necrotizing infundibular crystalline folliculitis , a folliculocentric disease first reported in 2001   on which only few data have been published . in a recently published study of denisjuk et al .
, 25 cases diagnosed in the past with necrotizing infundibular crystalline folliculitis ( as solitary lesions or accompanied by skin neoplasms ) or with ostiofolliculitis have been reviewed .
both sexes were equally affected ; most of them in the 50th decade and presenting lesions at the same predilection sites as acne , but clinically different from it .
it remains unclear whether the presence of malassezia plays a crucial role in the induction of crystalline structures   or mucin .
another possible mechanism inducing the crystalline material seems to be a chemical or physical injury . in our case ,
malassezia yeasts were abundant in the biopsy described above , but they were absent in biopsies of clinically identical lesions of the same patient with a much less characteristic histological aspect .
no bacteria have been observed in our case , and there were no anamnestic data including a possible chemical or physical injury . in the study of denisjuk et al .
, in 86% of all cases , yeasts and gram - positive bacteria corresponding to propionibacterium acnes have been identified .
pathogenetically these lesions may represent a perforating disorder , but some cases have shown a primary folliculocentric necrosis   rather than a primary perforating process .
sebum accumulation as nutrient medium for the microorganisms has been discussed , accompanied by the accumulation of crystalline material due to the destruction of tonofilaments and the degradation of lipids , followed by a rupture of follicular epithelia and accumulation of inflammatory cells .
histopathologically , the pathognomonic features are the birefringent urate - like crystals representing as alcian blue - positive filamentous mucinous material . on electron microscopy
, this crystalline material is composed of disrupted bundles of tonofilaments embedded in an amorphous matrix .
it was proposed that it represents monosodium urate   produced in the skin as a result of increased cell proliferation following local physical or chemical injury .
a surrounding inflammatory infiltrate was observed in our case , but this feature has not been reported in all of the cases described in the literature .
clinical response to topical or systemic antimycotic treatment suggests a role of malassezia yeasts in the pathogenesis of necrotizing infundibular crystalline folliculitis . in conclusion ,
our case is one more example of this exceptional lesion of as yet unknown etiology .
analysis of more cases will shed light on the understanding of the exact pathogenesis of this peculiar skin disease .
 necrotizing infundibular crystalline folliculitis is a rare follicular lesion of which the etiology is not well understood . 
 here we describe the case of a 71-year - old male patient presenting with multiple hyperkeratotic lesions localized on the forehead . 
 histopathological analysis of one of the lesions revealed a follicular invagination containing cellular debris and keratin lamellae containing filamentous mucinous material and numerous crystals birefringent in polarized light microscopy . 
Background
Methods
Results
Conclusion