By Tracey Vlahovic, DPM, FFPM RCPS (Glasg), Amanda Borrelli, DPM, MPH and Jessica Bruno, DPM
Disappearing nail bed is a diagnosis you have most likely never heard of but you see it in practice on almost a daily basis. It describes the entity in which long-standing onycholysis causes the nail bed to convert to digital skin, which ultimately results in nail plate shortening in comparison to the contralateral side due to lack of nail bed-nail plate attachment.1 The shortened nail will only grow so far distally and seem to stop, or it will abut the distal skin that becomes hypertrophied and deformed. Often, patients will complain of the lack of nail growth when comparing one foot to another and will relate pain at the distal tip of the toe where the nail meets the skin.
The nail may appear yellowish or white in color, or exhibit hyperkeratosis at the most distal edge. There might be a small bump or hypertrophy of the distal skin that deforms the distal tip of the toe. You may culture the nail but the culture results may come back as negative for fungal growth. However, you are confident visually that this is toenail onychomycosis. Before delving into this disorder, let us differentiate onycholysis from onychomycosis and discuss the pathophysiology behind it.
Understanding The Pathogenesis Of Onycholysis
Differentiating between onychomycotic and true onycholytic nail disorders is difficult for even the most seasoned practitioners. This can create issues when it comes to proper diagnosis and treatment plans. Having a strong understanding of the key characteristics of onychomycosis and onycholysis can help ensure proper identification of these nail disorders, and help reduce the amount of misdiagnosed culture-negative nails that receive incorrect treatment.
Onycholysis, separation between the nail plate and nail bed, is an early sign of onychomycosis, but not all nails that present with onycholysis are mycotic. Nails that have onycholysis without an underlying dermatophyte infection will not resolve with the use of an oral or topical antifungal. In my opinion, entertaining the wide-ranging differential diagnoses of onycholysis (such as onychomycosis, onychogryphosis, psoriatic nails, lichen planus-affected nails and trauma-induced pathology) and employing appropriate clinical laboratory testing are important to determine the source of onycholysis, and prevent the complication known as the disappearing nail bed.
From a microscopic perspective, the nail plate is made up of about 80 layers of keratinized flattened cells.2 There are three macroscopic layers that make up the nail plate: the dorsal layer, which is a few cells thick; an intermediate layer, which is the most flexible and thickest layer; and lastly, the ventral layer, which is only one or two cells thick.2 The nail matrix and nail bed comprise the layers beneath the nail plate. One can visualize the nail matrix proximally as a “half-moon” shape or lunula in some nails (hallux more so than the fifth digit). The nail matrix creates the nail plate.2
The nail bed begins from the distal edge of the lunula and extends all the way to the hyponychium distally. The nail bed lacks the keratin proteins K1 and K10 that are common in normal skin, and there is no granular layer like in the epidermis of normal or non-nail bed skin.2 The distal portion of the nail bed may have a different color in comparison to the rest of the nail bed and is usually a one to 1.5 mm transverse band of a deeper pink or brown.3 This is called the onychodermal band and is the first barrier present to prevent materials reaching underneath the nail plate.3
When there is a disturbance of the onychodermal band, a separation of the nail plate from the underlying nail bed may occur and this is known as onycholysis. Onycholysis typically originates at the distal free border of the nail plate and advances proximally. When onycholysis is present, the unattached nail plate will have a white appearance, whether it is in a linear streaking pattern or a geographic-like pattern. In the case of a dermatophyte invasion, the nail may present with yellow discoloration distally. If the onycholysis is present for an unknown period, the nail bed will become keratinized and develop dermatoglyphics, which ultimately results in what we know as the disappearing nail bed.4-7
Dr. Vlahovic is a Clinical Professor in the Department of Podiatric Medicine at the Temple University School of Podiatric Medicine in Philadelphia.
Dr. Borrelli is Chief Resident of the Podiatric Residency Program at CarePoint Health Hoboken University Medical Center in Hoboken, N.J.
Dr. Bruno is a third-year podiatric resident at Eastern Virginia Medical School in Virginia Beach, Va.
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2. Saner M, Kulkarni A, Pardeshi C. Insights into drug delivery across the nail plate barrier. J Drug Target. 2014;22(9):769-789.
3. De Berker D. Nail anatomy. Clin Dermatol. 2013;31(5):509-515.
4. Iorizzo M. Tips to treat the 5 most common nail disorders: brittle nails, onycholysis, paronychia, psoriasis, and onychomycosis. Dermatol Clin. 2015;33(2):175-183.
5. Perera E, Sinclair R. Diagnosis using the nail bed and hyponychium. Dermatol Clin. 2015:33(2):257-263.
6. Shemer A, Daniel 3rd CR. Common nail disorders. Clin Dermatol. 2013;31(5):578-586.
7. Jadhav VM, Mahajan PM, Mhaske CB. Nail pitting and onycholysis. Indian J Dermatol Venereol Leprol. 2009;75(6):631-633.
Editor’s note: This blog has been excerpted from the forthcoming feature article, “How To Address The Disappearing Nail Bed,” which will be published in the February 2021 issue of Podiatry Today.