Nail psoriasis

The diagnosis of nail psoriasis can be based solely on cutaneous and/or osteoarticular signs and symptoms if a confirmed diagnosis of psoriasis vulgaris exists¹³. In the absence of these signs, diagnosis can be complex and must rely on complementary examinations. Hyperkeratosis, onychorrhexis, nail plate discoloration, and nail plate thickening generally resemble onychomycosis, which occurs in up to 60% of patients¹³.

Nail unit involvement is characterized by pitting, rough and brittle nail plates, and pronounced transverse (Beau’s) lines¹⁴-¹⁶. Signs of nail bed involvement include distal onycholysis with a proximal yellow-orange margin and serrated border, splinter hemorrhages, oil-drop (salmon) patch, subungual hyperkeratosis, and red or black hemorrhagic spots¹⁴-¹⁶.

Nail pitting, distal onycholysis (separation of the nail plate from the underlying nail bed), oil-drop (salmon) patches, and splinter hemorrhages are key dermatoscopic features of nail psoriasis¹⁶,¹⁷. The formation of depressions, the characteristic nail pitting, is the most frequent finding and typically appears irregular on dermatoscopy, representing an indicative signal of nail psoriasis involvement (Fig. 2). This feature arises from parakeratosis of the nail matrix, leading to extrusion of parakeratotic cells as they emerge from beneath the proximal nail folds, thereby creating indentations on the nail surface¹⁴-¹⁶.

Figure 2 Clinical and dermoscopic image of nail psoriasis. 

The biopsy technique ideally indicated for the diagnosis of nail psoriasis is a punch biopsy without prior nail plate avulsion, as it preserves the morphology of the superficial tissue. However, it is difficult to introduce the punch through the nail plate while maintaining adhesion of the plate to the nail bed/matrix during instrument rotation without shear¹⁸. To reduce technical difficulty, the digit is soaked in warm water for a few minutes or the nail plate may be thinned by gentle abrasion¹⁹. Delay in performing the procedure and in specimen fixation can damage elements of the nail bed/matrix and compromise diagnostic accuracy²⁰.

In this regard, tangential excisional biopsy has gained prominence in the diagnosis of inflammatory nail diseases. In the tangential technique, the nail plate is carefully removed with a scalpel blade, preserving epithelial integrity and enabling artifact-free histopathological processing¹⁸. When bed and matrix alterations are present, a nail bed specimen is always preferable, both for technical ease and for a lower risk of scarring.

In a recent study by Bertanha et al. on tangential biopsy in nail psoriasis, good clinic-histopathological correlation was obtained using the following criteria: a mandatory criterion, dilated dermal papillary vessels, and at least three secondary criteria, namely, absence of spongiosis, presence of parakeratosis, psoriasiform epidermal hyperplasia, focal thinning of the granular layer and suprapapillary epidermis, and intra- or subcorneal neutrophilic exudate¹⁸.

Nail lichen planus (LP)

Nail involvement occurs in 10% of patients with LP. Early recognition is crucial, as the disease can inflict extensive damage to the nail matrix, resulting in anonychia and proximal pterygium²¹. Clinical features of nail LP include brittle, roughened nail plates, a red or mottled lunula, onychorrhexis (vertical ridging of the nail plate), and longitudinal striations²²,²³ (Fig. 3).

Figure 3 Nail lichen planus. 

Onychoscopy may aid in detecting early LP changes²²,²³. Nail-bed involvement is manifested by plate fragmentation, chromonychia (discoloration of the nail plate or subungual tissue), splinter hemorrhages, onycholysis, subungual hyperkeratosis, and longitudinal grooves²²,²³.

Twenty-nail dystrophy, or trachyonychia, is regarded as a variant of nail LP; its uniform appearance and the absence of proximal pterygium distinguish it from classic nail LP²¹. The idiopathic atrophic form presents acutely and typically progresses to diffuse nail destruction within a few months²¹.

The diagnosis of nail LP requires biopsy with clinic-histopathological correlation. Key histopathological features include hyperkeratosis, hypergranulosis, a band-like inflammatory infiltrate, basal cell degeneration, and pigment incontinence²⁴. In rare instances, subepidermal blister formation with prominent aggregates of colloid bodies may be observed, corresponding to the uncommon bullous variant of nail LP²⁴.

Onychomycosis

Onychomycosis is the most prevalent nail disease and can sometimes be confused with a variety of benign and malignant nail conditions²,²⁵. This nail disorder represents all fungal infections of the nails and may involve the nail bed, plate, and matrix. It is the most prevalent nail disorder, affecting toenails more frequently than fingernails due to slower growth, reduced blood supply, and prolonged exposure to dark, humid environments²⁵,²⁶.

Typical physical examination findings include hyperkeratosis of the nail bed, which often causes varying degrees of nail plate onycholysis²⁶. A white or yellow discoloration of the nail plate is common, as well as subungual debris²⁶. Trauma is a risk factor for onychomycosis, and violaceous/brown/black nail plate discoloration may also be present²⁶. In longstanding or severe cases, there may be extensive onychodystrophy with nail plate thickening, crumbling, ridging, onychocryptosis, and partial or complete nail loss²⁶ (Fig. 4). A dermatophytoma, or fungal abscesses, is a white/yellow or orange/brown longitudinal streak in the nail plate and is quite specific for onychomycosis²⁶.

Figure 4 Onychomycosis involving finger nails. 

Dermatoscopic features of onychomycosis include the “ruin appearance,” “longitudinal streaks,” and “spikes” at the proximal margin of the onycholytic area²⁷,²⁸. The “aurora borealis” sign (defined by the combination of multicolored chromonychia with longitudinal streaks, spikes, and onycholysis) demonstrates the highest sensitivity and specificity for this disorder²⁷,²⁸. The irregular, spiked proximal border corresponds to distal-to-proximal invasion of the nail bed’s longitudinal ridges by dermatophytes²⁷,²⁸.

Direct microscopy and fungal culture are the gold-standard methods for diagnosing onychomycosis²⁹. Microscopic examination is performed after the nail is cleaned with 70% isopropyl alcohol, and then subungual debris samples are obtained, typically 8-10 fragments, to improve diagnostic accuracy. In a positive direct examination and fungal culture, hyphae, pseudohyphae, and spores are identified, confirming infection, although the specific organism is not identified in direct microscopy only in culture examination²⁵,²⁹.

Nail biopsy is performed by obtaining a sample from the active site of infection, approximately 4 mm from the free edge³⁰. After paraffin embedding, the material is stained with hematoxylin and eosin and special fungal stains, periodic acid-Schiff and methenamine silver, to visualize fungal structures under microscopy³⁰. However, as with direct microscopic examination, histopathology should always be complemented by culture.

Paronychia

Paronychia is defined as inflammation or infection of the proximal or lateral nail folds³¹,³². Clinically, it presents with an acute onset of discomfort, tenderness, erythema, and edema. The acute form is characterized by disruption of the nail fold’s protective barrier and pathogen invasion³¹,³² (Fig. 5). Secondary infections often follow trauma, such as nail-biting or manipulation of ingrown nails, the latter being the most common etiologic factor³¹.

Figure 5 Paronychia involving both thumbs. 

If left untreated, infection may progress to the formation of granulation tissue around the nail fold and abscess development³¹. An untreated abscess in one fold can extend to involve all nail folds and may even spread into adjacent soft tissues of the affected digit³¹,³². Staphylococcus aureus is the primary pathogen, although Streptococcus spp., Pseudomonas spp., other Gram-negative bacteria, and Candida albicans can also invade the nail folds³¹,³².

Diagnosis of paronychia is primarily clinical, based on patient history and physical examination, which helps differentiate it from other nail disorders³¹-³³. For diagnostic confirmation, the digit-pressure test may be employed: when firm pressure over the affected fold produces an area of blanching larger than expected, an underlying abscess is likely present³¹-³³.

Paronychia can be classified as acute or chronic³¹,³³. In the acute form, physical examination may reveal a tender, erythematous, and edematous lateral nail fold, and if an abscess is present, a fluctuant area may be palpable³¹. In chronic paronychia, the nail fold may be red and swollen, but fluctuation is uncommon; the nail plate may become thickened and discolored, and proximal nail fold retraction, nail dystrophy, and cuticle loss can occur³¹.

Glomus tumor (GT)

GT is a benign vascular hamartoma originating from glomus cells, specialized smooth muscle cells concentrated around dilated vessels and this tumor present as red, purple, or blue lesions beneath the nail plate, classically characterized by the triad of pain, tenderness, and cold sensitivity³⁴,³⁵.

Clinical characteristics of GT typically appear as a small reddish-to-bluish macule under the nail plate or as longitudinal erythronychia with distal notching or fissuring of the nail plate³⁴ (Fig. 6). The predominant symptom is intense nail pain, which may be throbbing or pinpoint in nature; it can occur spontaneously or be provoked by pressure or cold exposure⁵,³⁴,³⁵.

Figure 6 Glomus tumor before and following nail-plate avulsion. 

GT are generally small and rarely palpable, rendering clinical examination inadequate for precise localization³⁶. Imaging studies facilitate accurate tumor localization and size assessment, critical factors in selecting the optimal surgical approach³⁶,³⁷. Nail-plate dermatoscopy may reveal vascular structures; however, these can sometimes be subtle or absent³⁶. Therefore, dermatoscopy of the nail bed and matrix before tumor excision is recommended, as it assists both in tumor localization and in visualizing the lesion’s vascular pattern³⁶.

Definitive diagnosis is established by performing a nail bed biopsy with nail plate avulsion. Histopathological examination demonstrates a variable admixture of glomus cells, vascular channels, and smooth muscle³⁸. GT are subclassified into three types: glomangiomas, marked by an abundance of vascular channels; solid GTs, composed predominantly of glomus cells; and glomangiomyomas, which show a predominance of smooth muscle elements³⁸.

Onychopapilloma

Onychopapilloma is a benign neoplasm of the distal matrix and nail bed, typically presenting as a longitudinal band of splinter hemorrhages associated with subungual hyperkeratosis³⁹ (Fig. 7). The most common dermatoscopic finding is longitudinal erythronychia, although melanonychia and a V-shaped distal nail-plate notch may also be observed³⁹.

Figure 7 Onychopapilloma. 

Histopathological examination features include subungual hyperkeratosis with or without focal hemorrhage; in excisional specimens, there is papillomatosis of the nail bed and acanthosis of the nail matrix with layers of subungual parakeratosis and focal parakeratosis³⁹.

Subungual melanoma (SM)

SM is a distinct subtype of cutaneous malignant melanoma that arises from the nail matrix. It is usually a variant of acral lentiginous melanoma, a form of melanoma originating in the palmoplantar region⁴⁰,⁴¹. In two-thirds of cases, SM presents as a longitudinal brown-to-black band on the nail plate, known as longitudinal melanonychia, but it may also be amelanotic and manifest as a red nodule⁴⁰,⁴¹. During its progression, periungual pigmentation may develop, known as Hutchinson’s sign, which, while not pathognomonic, is highly suggestive of melanoma, nail dystrophy may also occur, indicating more advanced disease⁴⁰. SM is often mistaken for an infection and initial misdiagnosis of SM occurs in 85% of cases⁴¹. Dermoscopy assists in distinguishing SM from benign melanocytic pigmented lesions, but biopsy remains the gold standard for diagnosis⁴¹.

Dermatoscopy can reveal a gray-brown to black background with longitudinal lines that are irregular in thickness, spacing, and color, as well as fine pigmented granules, features indicative of a melanocytic origin⁴⁰. The width of the pigmented bands can vary and may progress to total melanonychia⁴⁰.

Histologic features suggestive of malignancy include lesion asymmetry, infiltrative margins, a markedly increased number of melanocytes in the basal and suprabasal layers with a high propensity to form compact aggregates, presence of cytologic atypia, and dermal inflammation. Malignant melanocytes have large, atypical nuclei with increased mitotic activity. Identification of melanocytes in the nail plate is diagnostic of melanoma⁴². Invasive SM also exhibits irregularly dispersed dermal nests composed of atypical melanocytes⁴².

Squamous cell carcinoma (SCC)

SCC is the most common malignant tumor of the nail unit, with the in situ form (Bowen’s disease) occurring more frequently than the invasive variant and usually is associated with the Human Papillomavirus (HPV), mainly type 16, 18, 35, and 56⁴⁰,⁴³. It typically involves a single digit, most commonly the thumb⁴⁰,⁴³. The malignancy is usually indolent and painless, affecting the nail bed and periungual regions or both. Lesions are clinically classified into two main categories: periungual type, arising in the epithelium of the nail fold and sulcus and Subungual type, developing in the epithelium of the nail bed⁴⁰,⁴³.

Dermatoscopy of SCC is characterized by brown linear dots or a clustered glomerular vascular pattern⁴⁰. Other features include localized subungual hyperkeratosis, erythrochia or leukonychia irregular, lateral detachment (onycholysis), non-parallel longitudinal melanonychia, and splinter hemorrhages⁴⁰ (Fig. 8).

Figure 8 Clinical and dermatoscopical images of squamous cell carcinoma. 

Biopsy with histopathological examination is the gold standard for diagnosing SCC⁴⁰,⁴³. The histopathological characteristic findings of this tumor include loss of normal epidermal stratification, dyskeratosis, clusters of large cells with hyperchromatic nuclei, atypical mitosis, and, when associated with HPV, perinuclear vacuolization is typically observed⁴⁰,⁴³.

Onychocryptosis

Onychocryptosis, also known as ingrown toenails, is a condition in which the lateral nail fold is penetrated by the nail plate’s edge, causing pain and difficulty ambulating⁴⁴-⁴⁷. It is most common in adolescents, young adults, and males⁴⁴,⁴⁶. The penetration is often due to nail spicules along the plate’s margin, which elicit an inflammatory response⁴⁴,⁴⁶,⁴⁷. The great toes are most frequently affected⁴⁴.

The main causes include ill-fitting footwear, improper toenail trimming, abnormalities of the nail apparatus, and excessive perspiration⁴⁴,⁴⁷. The condition is unilateral in 80 % of cases and predominantly involves the hallux⁴⁴. Diagnosis of onychocryptosis is straightforward and classically based on clinical features, without the need for laboratory, radiographic studies, or dermatoscopy⁴⁴,⁴⁶,⁴⁷.

Patients typically present with toe pain that can range from mild discomfort when walking to complete inability to ambulate; depending on lesion progression, there may also be associated swelling, erythema, secondary infection, or seropurulent discharge⁴⁴-⁴⁷ (Fig. 9).

Figure 9 Onychocryptosis. 

Subungual hematoma (SH)

SH is a common nail lesion characterized by the accumulation of blood beneath a fingernail or toenail, typically located between the nail bed and the nail plate⁴⁸. Trauma is the principal etiology, and the migration of the hematoma distally with nail-plate growth serves as a key diagnostic feature⁴⁰,⁴⁸.

Clinically, the hallmark symptom is sudden, throbbing pain following nail injury, resulting from pressure exerted by the subungual blood collection⁴⁸. SH is the most frequent cause of bluish-red to bluish-black nail pigmentation; unlike melanocytic lesions, it does not form a continuous longitudinal band⁴⁰,⁴⁸,⁴⁹.

Dermatoscopic examination often reveals small, round blood globules at the periphery of the hematoma, distal streaking, and localized leuconychia at the trauma site, accompanied by a bluish-red, bluish-black, or brownish color coloration⁴⁰,⁴⁸,⁴⁹ (Fig. 10).

Figure 10 Clinical and dermatoscopy image of subungual hematoma.