The accessory nail of the fifth toe, also known as a double nail of the fifth toe (DNFT) [1] or a petaloid toenail, [2] is a physical trait of the small toe, where a minuscule sixth toenail is present in the outer corner of the nail situated on the smallest toe. Although understudied and underreported, its prevalence is common.
The accessory nail was first described in a 1969 paper by M. Hundeiker. [1] The trait can be observed on either one or both feet where there is a lengthwise separation of the toenail on the corner of smallest toe. The smaller sixth toenail separates from the main toenail on the outermost side of the foot, and protrudes outwards from the corner. [1] This nail averages 2–7 mm (0.079–0.276 in) in length. [3] The additional nail can be cut with a nail clipper. Its occurrence is considered common but underreported. [4]
The entire nail of the small toe is usually short and wide, and both nails often share the same nail bed. [4]
The cause is poorly understood due to a lack of research, but genome-wide scans indicate that it is a heritable trait, and could be autosomal dominant. [4] However, the wide variance in the size and structure of the accessory nail indicates that the trait may not follow a Mendelian pattern of inheritance, and may instead be a complex trait affected by multiple genes with minor genetic effects. [5]
In some cases, the accessory nail presents with an abnormal protrusion or distortion of the fifth distal phalanx, or the splaying or rotation of the toe or entire foot. The trait may be a mild form of hexadactyly. [4]
The condition may also appear following trauma to the toenail. [1]
Accesory toenails are often observed by the patient and diagnosed upon examination by a physician. X-rays are sometimes used to investigate the underlying bone structure for deformity. [4] Ena et al. proposed the diagnostic criteria have 4 components: presence at birth, potential inheritance, involvement of the fifth toe, and bilaterality. [6]
Differential diagnoses include trauma-induced short-term splits, ectopic nails, onychophosis, and calluses. [1] [3] [4]
Most people do not seek out treatment because the accessory nail typically does not cause pain or other symptoms that interfere with everyday activities. However, the condition can sometimes cause discomfort or pain, particularly when the accessory nail protrudes vertically from the nail bed. [4] For those who do choose treatment, an option is surgical or chemical matricectomy (complete removal or destruction of the nail matrix). [4] [2] [7]
Accessory toenails are observed in people from all ethnicities and races and are not more prevalent in one group than another. [4] The condition is equally as common in both males and females. [8]
They are stereotypically endemic to Han Chinese. [2] Studies have suggested its prevalence in certain parts of China to be between 51% and 79%. [8] [5]
Chinese mythology has it that during the time of the Yellow Emperor, there were two types of people living in China: those who were the descendants of the Yellow Emperor, and those who were nomadic Qiang people. The Henan people, led by Yin Wang, attacked the Qiang and abducted a Qiang woman, who later tried to escape. Yin Wang stabbed her in the abdomen as she tried to escape, so she gave birth to two children with a scar on the small toe of the foot. The children were taken back by Yin Wang for adoption, and their descendants were born with double nails on their small toes. [9]
Toes are the digits of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being digitigrade. Humans, and other animals that walk on the soles of their feet, are described as being plantigrade; unguligrade animals are those that walk on hooves at the tips of their toes.
A nail is a protective plate characteristically found at the tip of the digits of all primates, corresponding to the claws in other tetrapod animals. Fingernails and toenails are made of a tough rigid protein called alpha-keratin, a polymer also found in the claws, hooves and horns of vertebrates.
A nail disease or onychosis is a disease or deformity of the nail. Although the nail is a structure produced by the skin and is a skin appendage, nail diseases have a distinct classification as they have their own signs and symptoms which may relate to other medical conditions. Some nail conditions that show signs of infection or inflammation may require medical assistance.
Athlete's foot, known medically as tinea pedis, is a common skin infection of the feet caused by a fungus. Signs and symptoms often include itching, scaling, cracking and redness. In rare cases the skin may blister. Athlete's foot fungus may infect any part of the foot, but most often grows between the toes. The next most common area is the bottom of the foot. The same fungus may also affect the nails or the hands. It is a member of the group of diseases known as tinea.
An ingrown nail, also known as onychocryptosis is a common form of nail disease. It is an often painful condition in which the nail grows so that it cuts into one or both sides of the paronychium or nail bed. While ingrown nails can occur in the nails of both the hands and the feet, they occur most commonly with the toenails.
Paronychia is an inflammation of the skin around the nail, often due to bacteria or fungi.
Onychomycosis, also known as tinea unguium, is a fungal infection of the nail. Symptoms may include white or yellow nail discoloration, thickening of the nail, and separation of the nail from the nail bed. Fingernails may be affected, but it is more common for toenails. Complications may include cellulitis of the lower leg. A number of different types of fungus can cause onychomycosis, including dermatophytes and Fusarium. Risk factors include athlete's foot, other nail diseases, exposure to someone with the condition, peripheral vascular disease, and poor immune function. The diagnosis is generally suspected based on the appearance and confirmed by laboratory testing.
A subungual hematoma is a collection of blood (hematoma) underneath a toenail or fingernail. It can be extremely painful for an injury of its size, although otherwise it is not a serious medical condition.
Onychogryphosis is a hypertrophy that may produce nails resembling claws or a ram's horn.
Amorolfine, is a morpholine antifungal drug that inhibits Δ14-sterol reductase and cholestenol Δ-isomerase, which depletes ergosterol and causes ignosterol to accumulate in the fungal cytoplasmic cell membranes. Marketed as Curanail, Loceryl, Locetar, and Odenil, amorolfine is commonly available in the form of a nail lacquer, containing 5% amorolfine hydrochloride as the active ingredient. It is used to treat onychomycosis. Amorolfine 5% nail lacquer in once-weekly or twice-weekly applications was shown in two decades-old studies to be between 60% and 71% effective in treating toenail onychomycosis; complete cure rates three months after stopping treatment were 38% and 46%. However, full experimental details of these trials were not available, and since they were first reported in 1992 there have been no subsequent trials.
Angiofibroma (AGF) is a descriptive term for a wide range of benign skin or mucous membrane lesions in which individuals have:
Onychophosis is a localized or diffuse hyperkeratotic tissue that develops on the lateral or proximal nailfolds, within the space between the nailfolds and the nail plate, and is a common finding in the elderly. Onychophosis may involve the subungual area, as a direct result of repeated minor trauma, and most frequently affects the first and fifth toe.
Onychomadesis is a periodic idiopathic shedding of the nails beginning at the proximal end, possibly caused by the temporary arrest of the function of the nail matrix. One cause in children is hand, foot, and mouth disease. This generally resolves without complication.
Shell nail syndrome is a medical condition defined by the concurrence of large, rounded fingernails and bronchiectasis. Despite the visual similarity between the two conditions, shell nail syndrome and clubbed fingernails are opposites. Shell nail syndrome results from atrophy to the nail bed, whereas clubbed fingernails results from a bulbous, hypertrophic growth of soft tissue. The concurrence of the syndrome and bronchiectasis is well-established, however the exact causes of the deformity remains unknown. The syndrome has been observed affecting both the hands and larger toenails.
Melanonychia is a black or brown pigmentation of a nail, and may be present as a normal finding on many digits in Afro-Caribbeans, as a result of trauma, systemic disease, or medications, or as a postinflammatory event from such localized events as lichen planus or fixed drug eruption.
Pincer nails are a nail disorder in which the lateral edges of the nail slowly approach one another, compressing the nailbed and underlying dermis. It occurs less often in the fingernails than toenails.
Malalignment of the nail plate, also known as congenital malalignment of the great toenails or congenital malalignment syndrome, is a congenital malalignment of the nail of the great toe, and is often misdiagnosed although it is a common condition. It most commonly affects the halluces. The nail might be discolored and develop infections. If the misaligned nail becomes embedded in the lateral nail fold it can cause pain, inflammation and erythema.
Koenen's tumor (KT), also commonly termed periungual angiofibroma, is a subtype of the angiofibromas. Angiofibromas are benign papule, nodule, and/or tumor lesions that are separated into various subtypes based primarily on the characteristic locations of their lesions. KTs are angiofibromas that develop in and under the toenails and/or fingernails. KTs were once considered as the same as another subtype of the angiofibromas viz., acral angiofibromas. While the literature may still sometimes regard KTs as acral angiofibromas, acral angiofibromas are characteristically located in areas close to but not in the toenails and fingernails as well as in the soles of the feet and palms of the hands. KTs are here regarded as distinct from acral angiofibromas.
Surgical treatments of ingrown toenails include a number of different options. If conservative treatment of a minor ingrown toenail does not succeed or if the ingrown toenail is severe, surgical management by a podiatrist is recommended. The initial surgical approach is typically a partial avulsion of the nail plate known as a wedge resection or a complete removal of the toenail. If the ingrown toenail recurs despite this treatment, destruction of the germinal matrix with phenol is recommended. As an alternative, one may use 10% sodium hydroxide which is less toxic or trichloroacetic acid which may give faster healing time. Antibiotics are not needed if surgery is performed.
Efinaconazole, sold under the brand name Jublia among others, is a triazole antifungal medication. It is approved for use in the United States, Canada, and Japan as a 10% topical solution for the treatment of onychomycosis. Efinaconazole acts as a 14α-demethylase inhibitor.
