Answer to Image of the Month November 2015
Submitted by Mani Makhija, Urszula Carr and Steven Kossard
Necrotising infundibular crystalline folliculitis
Necrotising infundibular crystalline folliculitis (NICF) is a rare distinct disorder with characteristic clinico-histologic appearance. Histologically, it is a folliculocentric umblicated crater filled with filamentous material and capped by a parakeratotic column. The eosinophilic filamentous material is embedded in an amorphous matrix forming a plug on the infundibular ostia and bulging into the upper dermis. A vacuolar destruction of the surrounding follicle may be seen especially if actively looked for on serial or deeper sections. The lower part of the “crucible” is often bare and devoid of an epithelium. Unlike the present case which shows foamy macrophages flanking the lower edge of the lesion, the area often lacks significant inflammation. The crystalline material is negatively birefringent and on electron microscopy were noted to be tonofilaments. Immunohistochemistry with 34betaE12 (a cytokeratin) has been reported to be negative in one case report.
Clinically, the lesions occur in a wide age group with many occurring on the face and forehead. Cases have been reported on the neck, back and the nose as well. There are folliculocentric acneiform papules with sharply demarcated waxy, keratotic plugs. The condition has also been observed incidentally near skin neoplasms.
The condition was earlier believed to be a perforating disorder with urate-like crystals, however, the presence of focal necrosis of the follicle on histology and the presence of tonofilaments on ultrastructural analysis established this as a distinct form of folliculitis with unusual crystalline appearance, whose pathogenesis and course remains to be elucidated.
The proposed pathogenetic pathway is probably related to either a physical or chemical injury or to gram positive bacteria, Propionibacterium and Malassezia yeast in infundibulum and their complex interaction with lipids from sebum. Destruction of tonofilaments and degradation of lipids from sebum probably results in accumulation of filamentous material with birefringent crystals within the follicular ostia and infundibula causing or following rupture and inflammation.