Nailed it!

By Allison Evans, Assistant Managing Editor, January 1, 2025

Diagnosing conditions of the nail can be confounding. Patients may experience delays in treatment due to challenges in diagnosis. While the nail may seem like a cosmetic concern, nail diseases can impact daily activities and may even point to underlying systemic disease or infection. From nail psoriasis and nail lichen planus to retronychia and other nail conditions, there is a seemingly endless number of nail disorders — some with more distinctive clinical clues and others that are trickier to identify. In addition to clinical examination, dermoscopy, imaging, and histopathological and mycological testing may be necessary to confirm a diagnosis.

“Patients may come in specifically for a nail condition or the nail problem could be an incidental and may help confirm a skin disease such as psoriasis,” said Boni Elewski, MD, FAAD, James Elder professor and chair of dermatology at the University of Alabama. “Looking at the nail is very helpful in many situations. In general, a patient who presents with several abnormal fingernails may have an inflammatory process such as lichen planus or psoriasis but only one abnormal fingernail could be an infection or even a tumor. Onychomycosis is not common in the fingernails,” she said.

“Giving the wrong treatment for nails can really have disastrous consequences for patients, including the condition getting worse or missing a malignancy,” said Shari Lipner, MD, PhD, FAAD, associate professor of clinical dermatology, associate attending physician, and director of the Nail Division at the New York-Presbyterian Hospital/Weill Cornell Medical Center.

It’s critical for dermatologists to use their dermatoscope when examining the nail as there may be important clinical clues for diagnosis said Antonella Tosti, MD, FAAD, the Fredric Brandt Endowed professor of dermatology and cutaneous surgery at the University of Miami’s Miller School of Medicine. “For example, with onychomycosis, the main feature is onycholysis in a toenail. This could result from psoriasis, onychomycosis, trauma, a tumor, or many other things. But when you see spikes going proximally, this is a very typical sign for onychomycosis. If there is a tumor, you can sometimes see it with the dermatoscope.”

Nail psoriasis

Psoriasis most commonly affects the skin, and about 50-79% of patients have concurrent nail involvement. Five percent of patients with psoriasis have it only in the nails, with nothing on the skin. Nail psoriasis can be difficult to diagnose, particularly when a patient only has affected nails with limited or no skin involvement.

“With nail psoriasis, we often see nail plate pitting and onycholysis (the most frequent findings), splinter hemorrhages, and subungual hyperkeratosis. We can see nail bed thickening, and sometimes we have clues from the skin, including erythematous plaques with scale on the elbows and knees and other parts of the skin, and scale on the scalp,” Dr. Lipner said.

“In some instances, it may be difficult to clinically diagnose psoriasis — such as a person with scaly palms and soles since the differential diagnosis may include atopic eczema. Classic nail findings can clinically confirm the diagnosis of psoriasis,” explained Dr. Elewski. “Three nail signs of nail psoriasis include onycholysis with a red border, nail pitting, and oil spots.”

Pitting is not unique to nail psoriasis, although it probably occurs most commonly when nail psoriasis occurs, Dr. Elewski said. “You can also see pitting with alopecia areata, especially when the patient has alopecia totalis. Nail changes often indicate a bad prognosis for alopecia areata. When I have a patient come in with one round patch of hair loss, I still look at the nails and if there is no pitting, I get to tell the patient some good news — that they will likely have a short course.”

The pitting in nail psoriasis, however, is different than in alopecia areata. “In nail psoriasis, the pits are more irregular and a little larger, but it can still be hard to tell,” said Dr. Elewski. “It’s also important to look at the fingernails. Toenails don’t usually give us clues since they grow so slowly,” she added.

Onycholysis is also fairly common in nail psoriasis, and it can be due to trauma or contact dermatitis to nail products or something else entirely. But a red border indicates inflammation, which means it could be psoriasis, Dr. Elewski noted. “When the nail bed is involved, there may be a discoloration of the nail plate known as the “oil drop” sign or salmon patch. This looks like a reddish or salmon-colored spot under a nail and may occur with or without onycholysis,” she added.

It can be even trickier when a patient presents with only onycholysis, explained Dr. Tosti. It may be difficult to decide whether it’s due to trauma or nail psoriasis. “Here, dermoscopy can be very useful because you can look at the capillaries and the vessels of the hyponychium. With psoriasis, they can be enlarged and twisted, which can help you make the diagnosis. Otherwise, you can take a very small biopsy of the distal nail bed, which is a good way to confirm.”

Features of nail psoriasis



Onychomycosis

Onychomycosis is a fungal nail infection caused by dermatophytes, molds, and yeasts. It is the most common nail disorder, accounting for 50% of all nail disorders seen in clinical practice. Diagnosing onychomycosis is one of the easier diagnoses to make because it can be confirmed with a nail clipping and histopathology. “We can use KOH with microscopy, we can do a fungal culture, or use PCR testing,” Dr. Lipner said.

Many patients being treated for fungal infections have been diagnosed purely on clinical examination, noted Dr. Tosti. “You always need to have a laboratory test showing the presence of fungi. Most of these patients need to be treated with an oral treatment since topical therapeutics are only effective in about 20% of cases,” she added.

Onychomycosis most commonly affects the toenails, particularly the great toenail. Often tinea pedis accompanies onychomycosis. “A helpful clue could be scale on the plantar feet or in between the toes,” Dr. Lipner said. “There are a lot of ways to confirm the diagnosis. If I see a patient with a single fingernail affected, onychomycosis is lower on my differential diagnosis.”

Dermoscopy is a quick, non-invasive and highly effective diagnostic tool to help differentiate onychomycosis from other nail disorders. “Jagged proximal borders with spikes as well as longitudinal streaks are common features seen on dermoscopy, although mycological confirmation is still necessary since many nail conditions share clinical presentation similarities with onychomycosis,” Dr. Lipner said.

“Diagnosing other nail diseases, however, is much more difficult because we really have to rely mainly on clinical clues. Clippings could help in some cases to at least rule out onychomycosis or help us make a diagnosis of nail psoriasis, but there isn’t really a single feature or constellation of features that definitively makes the diagnosis,” Dr. Lipner explained.

Differential diagnoses for onychomycosis

Nail lichen planus

“Nail lichen planus is really an emergency for the patient; patients need prompt diagnosis and treatment to prevent permanent loss of nails,” said Dr. Elewski. “While you should look at the fingernails to observe the changes, it can occur in any nail. Some physicians may see nail lichen planus or nail psoriasis and assume incorrectly that it’s a fungus, but dermatophyte infection is extremely rare in the fingernails,” she emphasized.

“If you see someone with an abnormal fingernail, start thinking about psoriasis and nail lichen planus.” Dr. Elewski also recommends checking patients for lichen planus in the mouth.

Nail lichen planus is hard to diagnose because it’s rare, and often dermatologists don’t encounter this condition during residency. “Nail lichen planus looks different than nail psoriasis in most cases. With nail lichen planus, we often we see thinning of the nail or koilonychia, onychorrehexis (prominent ridges) and sometimes pterygium (scarring of the nail). In general, for nail lichen planus, the nail tends to look thinner while with nail psoriasis the nail tends to look thicker,” Dr. Lipner said. It can be progressive, and it can be progressive very quickly, she said.

It may also be misdiagnosed as trauma to the nail or even as brittle nail, Dr. Tosti added. “Always think lichen planus when you see multiple fissures and longitudinal ridging.”

At end-stage, patients may get pterygium, said Dr. Elewski. Once this occurs, there is no treatment — the nail won’t grow anymore. “Oftentimes, I’ll see children with longitudinal ridging of all 20 nails. This is called 20-nail dystrophy, or trachyonychia, in which the nails may be very thin and have ridging. This can be due to lichen planus or alopecia areata,” Dr. Elewski added.

“Another challenge in diagnosing nail lichen planus is that there aren’t histopathological features on a nail clipping to help you,” Dr. Lipner said. “Doing a clipping will rule out other conditions, but it won’t diagnose nail lichen planus. Nail experts generally recommend doing a longitudinal excision — so taking a sample that includes the nail plate, the nail bed, the nail matrix, and even parts of the hyponychium.”

“The question becomes: Are you biopsying the right nail and are you biopsying the nail at the right time,” Dr. Lipner added. “If it’s all burnt out, then you won’t see the lichenoid infiltrate.”

Retronychia

Retronychia, like lichen planus, is also a nail emergency and requires quick diagnosis and treatment. “Retronychia is like the opposite of an ingrown nail. It’s characterized by ingrowing of the nail plate into the proximal nail fold, and it’s likely due to trauma,” Dr. Elewski said. “The nail doesn’t fall off; instead, it hangs in, and another nail grows underneath it, which can create an oyster shell look with all the ridges.”

It’s more frequent in the great toenail than in fingernails and it’s often misdiagnosed as onychomycosis, paronychia, and sometimes nail psoriasis, said Dr. Lipner. “Patients have often been through the wringer of different treatments: oral treatments, topical treatments, laser treatment, and the nail just isn’t getting better.”

The diagnosis, Dr. Lipner said, is often determined by one question: Do your nails grow? When was the last time you clipped the nail? “Most of the time patients will say the nail doesn’t grow at all, or the last time they clipped it was two years ago. That’s a telltale sign that the patient has retronychia.”

For retronychia, ultrasound imaging can help confirm the diagnosis by better visualizing the defect under the proximal nail fold. Ultrasound imaging will reveal a thickened nail plate beneath the proximal nail fold while the presence of two or more superimposed nail plates will confirm the diagnosis (doi: 10.1080/07853890.2022.2044511). “However, we do not usually do this in clinical practice, and most radiologists are not trained in nail ultrasound,” said Dr. Lipner.

“You may see xanthonychia, which is the yellowing of the nail plate. You can see overlapping nail plates — and when it’s longstanding, often the nail bed will be shortened,” Dr. Lipner added.

If a dermatologist is sure that they’re diagnosing retronychia, Dr. Lipner discourages doing a nail clipping. Sometimes the clipping can be misleading since the nail is stagnant. “Yeast or fungus can colonize and secondarily infect the nail, so you may have retronychia and a clipping that shows fungus. Don’t bother treating the fungus because as long as the nail is stuck in place, no antifungal is going to make that nail better.”

Contact dermatitis

Another commonly misdiagnosed nail disorder is contact dermatitis of the nail, said Dr. Tosti. “It is not uncommon to see in people who use gel or acrylic nails. When you see psoriasiform and eruptions limited to the fingernails, it’s important to consider allergic contact dermatitis,” she added.

“Patients may develop inflammation of the nails or detachment of the nail plate, and it is often misdiagnosed as nail psoriasis or trauma. Many times, patients don’t provide accurate histories, and they won’t think to tell you that it occurred after doing a gel manicure,” Dr. Tosti said. Many patients are trying to save money by doing gel manicures themselves at home. “When you do this, you have greater exposure to the chemicals than in the salon,” Dr. Tosti said.

Other people may come in with contact dermatitis due to nail polish. This can cause onycholysis, which will be in the shape of the outline of the nail plate, Dr. Elewski said. It might be contact dermatitis to nail polish, acrylic nails, or some other nail product. “I used to see a lot of this when formaldehyde or nickel was put in nail polish, which has now become less common.”

Other conditions of note

Another condition that may trip up dermatologists is onychopapilloma, which is a benign nail tumor. “The clue of an onychopapilloma is that the patient has a fairly thin 1-to-2-millimeter longitudinal red line in the nail. Now, there’s a broad differential for longitudinal retronychia, but the key to making the diagnosis of onychopapilloma is, number one, that the band starts in the lunula, and number two, there’s a hyperkeratotic papule at the hyponychium. You may not see it with the naked eye, but if you use your dermatoscope end on with ultrasound gel, you can see the papule, and then it’s easy to make the diagnosis. However, definitive diagnosis is with a biopsy with histopathology.” Dr. Lipner said.

“The nail glomus tumor can present similar to onychopapilloma in that it presents with a red line. But it can also present with a blue macule that’s seen through the nail plate, so there are two different presentations,” Dr. Lipner said. “What’s distinctive about glomus tumors is that they’re so painful. You can’t forget the patient that says, ‘my nail is painful.’ It can be subtle, and you really have to look for that red line or that blue macule when the patient presents with pain.”

There are imaging tests that can help, Dr. Lipner added. “Sometimes you can get an X-ray, and it will show erosions in the bone. But a glomus tumor has to be in the right place, and it has to be big enough for you to see the bone erosion. Often, X-rays are negative. You can also order an MRI with contrast, but a more cost-effective option is ultrasound, both tests which can be done for glomus tumors that are two millimeters or less.”

For Dr. Tosti, onychotillomania, or when people damage their own nails, is one of the most common misdiagnosed conditions that she encounters. “Sometimes this is thought to be an infection, and a dermatologist may prescribe something like cyclosporine. You may also find inflammatory pigmentation because in inflammatory nail disorders you may have melanonychia or longitudinal pigmentation of the nail due to activation of melanocytes.”

In a JAAD study characterizing the most common dermatoscopic features of onychotillomania in 36 patients, 69.4% had wavy lines (uneven longitudinal lines in different planes with a wavy appearance from uneven nail plate growth), 63.9% obliquely oriented nail bed hemorrhages, and 47.2% nail bed gray discoloration. These changes were not seen in nail lichen planus, nail psoriasis, or onychomycosis (doi: 10.1016/j.jaad.2018.04.015).

Nail unit squamous cell carcinoma is called the “great mimicker,” said Dr. Lipner. “It can look like anything: a wart, pyogenic granuloma, onychomycosis, or nail psoriasis. If you see a patient with a nail finding and they’re not responding to treatment, you checked for hyphae or fungus, it’s getting worse, and it involves a single nail, then I think it’s important to do a biopsy.”

It is important to look at the nails in all patients who come to your office, Dr. Elewski said. “When someone presents with abnormal fingernails, look at the toenails. If someone presents with abnormal toenails, look at the fingernails.”

“You use your nails every single day for various activities, including walking, not to mention the cosmetic concerns many patients may have. Nails are very important for our patients, making it critical that we take the time to closely examine them,” Dr. Tosti said.

Additional DermWorld Resources