Inverted Follicular Keratosis

Overview
Inverted follicular keratosis  a benign usually solitary epithelial tumor originating in a hair follicle and occurring as a flesh-colored nodule or papule.

Inverted follicular keratosis is believed to be an inflammatory variant of seborrheic keratosis. It commonly is found on the faces and sun-exposed areas of elderly patients. Typically, this lesion is located on the upper eyelid. Anatomically, it represents an upside-down or endophytic process within the epithelium of a pilosebaceous follicle. The lesions tend to be single and present as a papule or nodule.

Etiology

This is an acquired lesion, similar to seborrheic keratosis.

Histology

The hallmarks of this lesion are the plentiful squamous eddies. A papillomatous and acanthotic appearance is found reliably. The margins are discrete and lack the inflammatory component found in keratoacanthoma.

Treatment

Since this lesion is benign, simple excision is adequate.

To facilitate accurate communication of the description of skin lesions between medical personnel, a multitude of descriptive terms have been developed. The terminology can largely be categorized as gross morphologic or histological descriptions. The purpose for these potentially confusing terms is to describe an oftentimes complex visual finding into verbal and written form. This process is further complicated by the lack of uniformity in the literature regarding some of the term definitions. The following list of commonly used descriptive terms presents their most commonly accepted definitions. Note that some of the terms can be used to describe both a morphologic and a histologic finding; such terms are denoted with an asterisk.

Gross morphologic terms

• Blister - Nonspecific term for fluid-filled lesion (see vesicle or bulla)
• Bulla - Fluid-filled lesion >5 mm in greatest dimension
• Excoriation - Lesion of traumatic nature with epidermal loss in a generally linear shape
• Lichenification * - Grossly thickened, leathery, hyperpigmented skin with hyperkeratosis and deep, widely-spaced skin markings
• Macule - Flat circumscribed area demarcated by color from surrounding tissue
• Nodule - Solid raised discrete lesion >5 mm in greatest dimension
• Onycholysis - Loosening or loss of nail substance resulting in loss of integrity
• Papule - Solid raised discrete lesion £ 5 mm
• Pedunculated - Attached to its base by a stalklike structure
• Plaque - Flat but elevated area, usually >5 mm
• Pustule - Small pus-filled elevated area of the skin with discrete borders
• Seborrheic - Related to excessive secretion of sebum
• Sebum - Thick, greasy substance secreted by sebaceous glands that consists of fat and cellular debris
• Sessile - Attached directly to the skin by a broad base; not pedunculated
• Vesicle - Fluid-filled lesion £ 5 mm

Histologic terms

• Acantholysis - Dissolution of intercellular integrity with fragmentation of epidermis
• Acanthosis - Hyperplasia of epidermal layer
• Dyskeratosis - Abnormal keratinization occurring prematurely in cells below the stratum granulosum
• Erosion - Loss of epidermis
• Exocytosis - Infiltration of epidermis by inflammatory cells
• Hyperkeratosis (keratosis) - Thickening of the stratum corneum (the outermost layer of the epidermis) with excess abnormal keratin
• Lichenification * - Hyperplasia of all compartments of the epidermis with acantholysis and papillomatosis
• Papillomatosis - Hyperplasia of the papillary dermis and lengthening and/or widening of the dermal papillae
• Parakeratosis - Persistence of the nuclei within the cells of the stratum corneum of the epidermis as seen in psoriasis
• Spongiosis - Edema limited to the epidermis
• Ulceration - Loss of epidermis with variable partial-to-complete loss of dermis

Other terms

• Acral - Related to the extremities and the more distal parts of the body
• Actinic – Relating to biochemical changes in the skin produced by sunlight energy from both the visible and ultraviolet rays

Keratosis follicularis (Darier-White disease) is a genetic disorder of abnormal keratinization and is inherited in an autosomal dominant pattern.

Keratosis follicularis is characterized clinically by scaly, warty, crusted papules distributed mostly on the seborrheic areas of the body. Nail involvement is characterized by V-shaped nicking at the distal aspect of the nail bed, longitudinal red and white alternating bands, and subungual hyperkeratosis (buildup of scales underneath the nailplate). Mucosal membrane involvement may occur as white papules on the buccal mucosae, palate, and gingiva with a cobblestone appearance.

Physical examination classically shows keratotic papules that are distributed mostly on the so-called "seborrheic" areas of the body.

Nail involvement is not uncommon and is characterized by V-shaped nicking at the distal aspect of the nail bed, longitudinal red and white alternating bands, and subungual hyperkeratosis.

The mutation has been traced to chromosome 12, where a spectrum of mutations within the ATP2A2 gene encode the calcium ATPase of the sarco/endoplasmic reticulum (SERCA2).