When A Runner Presents With Painful Plantar Lesions
A Closer Look At Porokeratosis Plantaris Discreta
Porokeratosis plantaris discreta, also known as Steinberg’s lesion, is a skin condition that occurs in adults with a 4:1 female preponderance.1 Steinberg first described the lesions in 1951 and he and Taub published the first research on the condition.2 Steinberg described the presence of a crater-like aperture that was apparent in some cases of plantar hyperkeratosis when the callus underwent debridement. The aperture contained keratin material and formed a horny plug that was attached to the under surface of the callus. He labeled the aperture a plugged cyst, assuming that it was a dilated or enlarged eccrine gland duct.
The lesions are characterized by an area of hyperkeratotic tissue with a central nucleated core that has a white or yellow-white appearance. There is tenderness with side-to-side compression of the lesion. The lesions likely develop as a result of direct pressure on the plantar surface of the skin but are not usually associated with an underlying osseous condition.3 There is still some debate as to whether the underlying ducts of sweat glands are involved.
Histologic examination reveals a cornoid lamella and transepidermal elimination of blood vessels and collagen fibers, which may be caused by the acceleration of keratinization. The pain and tenderness may have been partially related to epidermal disruption.4
Rabinowitz completed a histological evaluation and reported that porokeratosis plantaris discreta is essentially a clavus.5 Cystic sweat duct dilation, previously considered to be of paramount diagnostic significance, is not consistently found in porokeratosis plantaris discreta and is present in a variety of unrelated lesions.
One should differentiate porokeratosis plantaris discreta from other porokeratoses. The cornoid lamella with porokeratosis plantaris discreta is a broad solid keratin plug. With other variations of porokeratoses, the cornoid lamella has more of a centrifugally enlarging annular or serpentine ridge.
In 1990, Yanklowitz and Harkless examined 18 specimens from six patients with so-called porokeratosis plantaris discreta.6 They utilized light and electron microscopy, and the diagnosis was based on the classic descriptions by Taub and Steinberg.2 Yanklowitz and Harkless indicated that the findings in their study did not corroborate with the findings of Taub and Steinberg.
Based on this study and a review of current literature at that time, Yanklowitz and Harkless suggested discontinuing the use of the diagnostic term porokeratosis plantaris discreta.2 However, the term porokeratosis plantaris discreta continues to be used today in the medical literature.
A Guide To The Differential Diagnosis
There are a number of lesions that develop on the plantar aspect of the foot that are often difficult to distinguish from each other, possibly resulting in an incorrect diagnosis and treatment failure.
Plantar verrucae. Plantar verrucae or plantar warts are very common lesions that are caused by infection of epidermal keratinocytes by human papilloma virus. A breach in the integrity of the skin results in epidermal inoculation, which allows the virus to reach the level of the stratum terminative. This results in overproliferation of the virus cells and the development of the benign skin lesion.7
Plantar verrucae develop on all surfaces of the foot and are distinguished by the absence of skin striations and the presence of papillary formation within the lesion, which gives it a peppered appearance. A reactive callus will form on the weightbearing areas of the plantar foot, resulting in pain with standing and ambulation. Treatment options include excision, laser destruction or topical agents.8