The fully keratinized, thick multilayered structure of the nail plate presents a formidable barrier to nail bed access. This limits the options for treatment of nail diseases such as onychomycosis and subungual hematoma from nail trauma. Until recently, clinicians considered nail removal as an option for formal repair of the nail bed for subungual hematomas involving large regions of the nail bed.1
Penetration enhancing formulations have aided the delivery of molecules to the nail bed through the impermeable nail plate.2 Researchers have used a carbon dioxide laser to treat pincer nail deformity.3 Other authors have demonstrated the use of nail abrasion via sanding of the nail plate to decrease the nail thickness or remove the nail plate completely to facilitate penetration of topical medicines.4 However, these uncontrolled methods cause significant discomfort and may lead to structural deformities in the nail plate.
Podiatrists and dermatologists are also using nail trephination or nail punch biopsy to treat several nail abnormalities. Researchers have shown that mesoscissioning provides a controlled, painless way of creating openings in the nail plate. These microscopic openings, called transungual microconduits, are less than 0.5 mm in diameter and offer minimally invasive access to the nail bed.
The PathFormer (Path Scientific), a handheld device that operates on the mesoscissioning principle, allows one to trephinate the nail virtually painlessly, according to one completed pilot clinical trial and a second ongoing, double-blind clinical trial. This device, which is approved by the Food and Drug Administration for controlled nail trephination, has the potential to transform the treatment of nail disease ranging from subungual hematomas to onychomycosis.
A Closer Look At Mesoscissioning Technology
Mesoscissioning technology uses a microscopic cutter to scission (or cut) a circular opening in the nail plate. The keratinized nail plate has a high electrical resistance. As the cutter progresses into the nail plate, it removes successive layers of the nail plate and accordingly decreases the electrical resistance to the epidermis. The resistance can reduce from a few megaohms for an intact nail plate to tens of kilohms for an opening extending to the stratum corneum free nail bed. Mesoscissioning exploits this reduction to limit the intervention depth and thus avoids reaching the underlying innervated nail bed.
The result is a virtually painless procedure that creates a well defined microscopic hole in the nail plate. By varying the trigger resistance at which one pulls the cutter away from the nail, physicians can intervene superficially, partly, halfway or all the way into the nail plate.
The PathFormer device contains two micromotors. One rotates a 400 micron diameter cutter that scissions the nail plate and the other moves the cutter towards or away from the nail. The cutting motor is connected to an electronic control that measures the electrical resistance between the rotating cutter and an electrode one places on the patient’s skin. The cutter abruptly stops and retracts from the nail when one has reached a preset resistance, leaving a cylindrical microconduit in the nail plate.
The PathFormer cable connects to a pair of monitoring electrodes on the patient’s skin and the power supply unit clips to the operator’s belt. The physician presses and holds down the actuating button until the cutter automatically pulls away from the nail after creating a microconduit. The scissioning time is approximately two seconds.
In one case, surgeons created typical transungual microconduits in a human volunteer toenail using a PathFormer. The surgeon created four microconduits, approximately 400 microns in diameter and about 2 cm apart. The bottom of a newly created microconduit is soft but it slowly hardens over a period of 24 hours. However, hydrating the toenail and keeping it occluded (with a non-porous Band-Aid) prevents the microconduit bottom from hardening.
Emphasizing The Painless Nature Of The Procedure
A phase I study conducted at Brigham and Women’s Hospital (Boston) demonstrated that the mesoscissioning procedure causes virtually no pain.5 This study involved creating five microconduits of different depths in the great toenail in healthy volunteers using the PathFormer device. The microconduit depths ranged from the nail plate surface to the nail bed.
All 14 participants in the trial rated the pressure and pain sensation to be less than 3 (on a 1-10 scale with 10 indicating the highest degree of pain).5 This study also demonstrated that the depth control offered by the PathFormer is effective in a diverse population.
Facilitating More Effective Results With Subungual Hematomas And Onychomycosis
Subungual hematoma, commonly referred to as black toe, is an accumulation of blood in the space between the nail plate and the nail bed. Such injuries result from crushing of the nail against a hard surface and are common in long distance runners. The pressure generated from the accumulated blood can cause intense pain. Decompression of the hematoma can produce immediate relief. However, the decompression methods currently available can cause a significant amount of discomfort. Present treatment options include creating an opening in the affected nail with a heated paper clip or with an electrocautery device.
The trephination device can create one or more microconduits in the affected area to drain the pooled blood.6 Blood flows freely from the openings as soon as the cutter scissions through the nail plate. The procedure causes minimal, momentary discomfort with no side effects.
Onychomycosis is the most common disease of the nails and affects nearly 15 percent of the general population. Treatments include systemic therapy, topical treatment and nail avulsion by surgical or chemical means.7 Systemic therapy may lead to hepatotoxicity and drug interactions in patients receiving multiple medications.8 Topical medication to treat nail fungal infection is largely ineffective as it does not penetrate the nail plate well enough to reach the nail bed where the fungal organisms reside.
Microconduits provide an effective delivery route to the nail bed for the topical medications. Researchers conducted a double-blinded phase I clinical trial using the mesoscissioning technique in 28 patients with great toenail onychomycosis. Following the initial trephination, patients applied topical terbinafine (Lamisil, Novartis) cream or a placebo to the affected toenail twice daily for 24 weeks. Preliminary results suggest that nail trephination aids in medication delivery to the nail bed with 71 percent of patients showing improvement in clinical assessment in comparison to 28 percent in the placebo group.9
The transungual microconduits created by the PathFormer are less than 0.5 mm in diameter and are inconspicuous. The microscopic size of these openings also limit potential for infection or structural deformity of the nail. All the participants in a phase I trial agreed that the mesoscissioning procedure is painless and minimally invasive. The preoperative and operative procedures for creating these microconduits are simple and rapid, and physicians can easily perform them in the office.
1. Baran R. Fitzpatrick’s Dermatology in General Medicine, 6th ed. New York: Mcgraw Hill, 2003: 2585-94.
2. Hui X, Shainhouse Z, Tanojo H, et al. Enhanced human nail drug delivery: nail inner drug content assayed by new unique method. J Pharm Sci. 91(1):189-195, 2002.
3. Lane JE, Peterson CM, Ratz JL. Avulsion and partial matricectomy with the carbon dioxide laser for pincer nail deformity. Dermatol Surg. 30(3):456-458, 2004.
4. Chiacchio ND, Kadunc BV, de Almeida ART, Madeira CL. Nail abrasion. J Cosmetic Derm. 2:150-152, 2004.
5. Ciocon DH, Gowrishankar TR, Herndon TO, Kimball AB. How low should you go: novel device for nail trephination. Derm Surg. 32(6): 828-833, 2006.
6. Salter SA, Ciocon DH, Gowrishankar TR, Kimball AB. Controlled nail trephination for subungual hematoma. Am J Emerg Med (in press).
7. Bodman MA, Feder L, Nace AM. Topical treatments for onychomycosis: a historical perspective. J Am Pod Med Assoc 93(2):136-141, 2003.
8. Katz HI, Gupta AK. Oral antifungal drug interactions: a mechanistic approach to understanding their cause. Dermatol Clin. 21(3):543-563, 2003.
9. Boker A. A randomized, double-blind, placebo-controlled, pilot study of 1% terbinafine cream applied twice daily and delivered via nail plate microporation for the treatment of subungual toenail onychomycosis. Poster P1507, presented at the 2007 American Academy of Dermatology Annual Meeting, Washington, D.C. February 2007.