**8. Differential diagnosis of nail psoriasis**

There is a wide range of potential differential diagnoses, the most important of which are onychomycoses (Table 2) and nail dystrophies after minor trauma, in chronic venous insufficiency and impairment of the peripheral circulation.

**Onychomycoses** are the most frequent nail disorders. Distal and distal-lateral subungual onychomycosis (DLSO) are mainly due to dermatophytes with *Trichophyton rubrum* being the most frequent pathogen although T mentagrophytes (interdigitale) also plays an important role. All other dermatophytes are rather rare and the role of most yeasts and nondermatophyte moulds as primary nail pathogens remains disputed. DLSO begins at the hyponychium from where the fungus slowly invades the nail bed in the direction toward the matrix. The infection apparently irritates the nail bed epithelium that produces a reactive hyperkeratosis, which harbours most of the fungal elements whereas the nail plate rather acts as a barrier. In contrast to psoriatic onycholysis that exhibits the classical salmon spot colour at its proximal margin, mycotic onycholysis has no reddish-brown margin (Fig 21 a&b). Nail psoriasis and onychomycosis may coexist (Natarajan et al, 2010).


Table 2. Differential diagnostic clinical signs in onychomycosis (OM) and nail psoriasis

is graded from 0 to 4 and body surface is divided into ten areas and each is quantified. The

There is a wide range of potential differential diagnoses, the most important of which are onychomycoses (Table 2) and nail dystrophies after minor trauma, in chronic venous

**Onychomycoses** are the most frequent nail disorders. Distal and distal-lateral subungual onychomycosis (DLSO) are mainly due to dermatophytes with *Trichophyton rubrum* being the most frequent pathogen although T mentagrophytes (interdigitale) also plays an important role. All other dermatophytes are rather rare and the role of most yeasts and nondermatophyte moulds as primary nail pathogens remains disputed. DLSO begins at the hyponychium from where the fungus slowly invades the nail bed in the direction toward the matrix. The infection apparently irritates the nail bed epithelium that produces a reactive hyperkeratosis, which harbours most of the fungal elements whereas the nail plate rather acts as a barrier. In contrast to psoriatic onycholysis that exhibits the classical salmon spot colour at its proximal margin, mycotic onycholysis has no reddish-brown margin (Fig 21

**Onychomycosis Psoriasis** 

Frequent Less frequent

rare

Rare

periungual psoriasis

Frequent familiarity, particularly in early onset psoriasis and HLA-Cw6

positive subjects

alterations

Finger nails more often affected by psoriatic

a&b). Nail psoriasis and onychomycosis may coexist (Natarajan et al, 2010).

Pits Rare Very frequent Onycholysis Frequent Frequent Discoloration Yellow – brown None - yellow

Fungi Very frequent, depends on type of OM

infected

Heredity Autosomal dominant

Transverse ridges Rare Rare Splinter haemorrhages Almost never Rare Leuconychia Depends on onychomycosis type:

Superficial white OM

Proximal white subungual OM

Paronychia In onychomycoses due to moulds In psoriatic arthritis and

Toe nails 7 to 10 times more often

Other skin lesions Tinea pedum and/or manuum Psoriasis elsewhere

Table 2. Differential diagnostic clinical signs in onychomycosis (OM) and nail psoriasis

susceptibility to get a dermatophyte nail infection

XL-PASI scale ranges from 0 to 148 (Wittkowski et al, 2011).

insufficiency and impairment of the peripheral circulation.

**8. Differential diagnosis of nail psoriasis** 

Loss of nail transparency

Finger vs. toe involvement

Fig. 21. Psoriatic onycholysis demonstrates a livid-red proximal margin (A), which is not seen in mycotic onycholysis (B).

There are also many histopathological signs in common of onychomycosis and nail psoriasis (Table 3). This may render the differential diagnosis between these two frequent nail conditions very difficult if not impossible. Furthermore, it is possible that both onychomycosis and psoriasis are present in the same subject in different digits as well as in the same nail (Fig.22). It is therefore self-evident that a specimen sent for histopathological diagnosis of nail psoriasis is also stained with periodic acid-Schiff (PAS) or another fungal stain like silver-methene amine (Grocott).

Nail Psoriasis 165

Reiter's disease is an infrequent reactive arthritis with changes of the ocular, genital and oral mucosae such as conjunctivitis, blepharitis, scleritis or iridocyclitis, balanitis, vulvitis or stomatitis circinata, which are virtually indistinguishable from lingua geographica and its very rare extralingual analogues, and painful inflammation of joints and the vertebral column. Many patients are HLA-B27 positive. Nail changes often start with pits and salmon patches remaining indistinguishable for a long time from nail psoriasis (Pajarre et al, 1977,

Lovy et al, 1980) before the nails become destroyed (Fig. 23) (Table 4).

Fig. 23. Reiter's disease of the nails (Courtesy T Ruzicka, Munich)

Pitting Very frequent Less frequent Onycholysis Frequent Frequent Subungual keratosis Variable Pronounced Salmon patch Reddish More brown Nail destruction Rare Marked

Skin lesions elsewhere

**Psoriasis Reiter's disease** 

Table 4. Differential diagnosis of nail psoriasis and nail changes in Reiter's disease

Onycholysis is often due to overzealous manicure, but psoriasis of the nails renders them more susceptible to develop onycholysis due to minor trauma. Again, psoriatic onycholysis has usually a reddish proximal margin, which is lacking in onycholysis semilunaris (Fig. 24). Eczema involving the nail apparatus usually causes pit-like depressions leading to a rough nail surface called trachyonychia as well as to irregular transverse lines. The depressions are commonly less deep and less regular in size than in psoriasis. Although these depressions are more common in allergic contact dermatitis and nummular eczema they are also seen in atopic eczema (Nnoruka et al, 2004). Despite the trachyonychia, the nail may still retain its shine. In contrast, subungual contact dermatitis, e.g. as seen in acrylate allergy, causes

Frequent Palmar and plantar lesions, joint changes, mucosal lesions

Fig. 22. This nail histopathology shows both psoriasis and onychomycosis: on the surface, 2 pits are seen; the nail itself is a bit wavy and displays fungal hyphae seen as fine eosinophilic lines in the deep layer of the nail in this haematoxylin & eosin stain section; at the undersurface of the nail there is loose keratin, which is mostly parakeratotic and contains several Munro's microabscesses.


Table 3. Histopathological differential diagnosis of nail psoriasis and onychomycosis

Fig. 22. This nail histopathology shows both psoriasis and onychomycosis: on the surface, 2

eosinophilic lines in the deep layer of the nail in this haematoxylin & eosin stain section; at the undersurface of the nail there is loose keratin, which is mostly parakeratotic and

> with accumulation of neutrophils and serum

mononuclear exocytosis

Surface alterations Usually not present Cup-shaped depression of

subungual hyperkeratosis and undersurface of nail

Table 3. Histopathological differential diagnosis of nail psoriasis and onychomycosis

globules

of nail bed

**Onychomycosis Psoriasis** 

Marked hyperkeratosis with accumulation of neutrophils and serum

Papillomatous hyperplasia

mononuclear exocytosis

nail plate surface with parakeratosis: psoriatic pit

May be present in double

globules

of nail bed

pathology

Spongiosis and

Patchy hypergranulosis Patchy hypergranulosis

pits are seen; the nail itself is a bit wavy and displays fungal hyphae seen as fine

contains several Munro's microabscesses.

Nail bed and matrix

granulosis

Subungual hyperkeratosis Marked hyperkeratosis

Nail bed hyperplasia Papillomatous hyperplasia

Spongiosis and exocytosis Spongiosis and

Demonstration of fungi Hyphae and spores in

plate

Reiter's disease is an infrequent reactive arthritis with changes of the ocular, genital and oral mucosae such as conjunctivitis, blepharitis, scleritis or iridocyclitis, balanitis, vulvitis or stomatitis circinata, which are virtually indistinguishable from lingua geographica and its very rare extralingual analogues, and painful inflammation of joints and the vertebral column. Many patients are HLA-B27 positive. Nail changes often start with pits and salmon patches remaining indistinguishable for a long time from nail psoriasis (Pajarre et al, 1977, Lovy et al, 1980) before the nails become destroyed (Fig. 23) (Table 4).

Fig. 23. Reiter's disease of the nails (Courtesy T Ruzicka, Munich)


Table 4. Differential diagnosis of nail psoriasis and nail changes in Reiter's disease

Onycholysis is often due to overzealous manicure, but psoriasis of the nails renders them more susceptible to develop onycholysis due to minor trauma. Again, psoriatic onycholysis has usually a reddish proximal margin, which is lacking in onycholysis semilunaris (Fig. 24).

Eczema involving the nail apparatus usually causes pit-like depressions leading to a rough nail surface called trachyonychia as well as to irregular transverse lines. The depressions are commonly less deep and less regular in size than in psoriasis. Although these depressions are more common in allergic contact dermatitis and nummular eczema they are also seen in atopic eczema (Nnoruka et al, 2004). Despite the trachyonychia, the nail may still retain its shine. In contrast, subungual contact dermatitis, e.g. as seen in acrylate allergy, causes

2010).

and Dawber, 1987).

**9.1 Topical therapy** 

**9. Treatment of nail psoriasis** 

serious impact on the individual's daily life.

applying a specific therapy, and not the least also on its cost.

Nail Psoriasis 167

Irritant contact dermatitis was also estimated to mimic nail psoriasis (Takeuchi et al,

Alopecia areata is known to be associated with rough nails. The more extensive the alopecia areata is the more likely the patients also get nail changes. Most probably, isolated alopecia areata of the nails does exist (Tan et al, 2002, Nanda et al. 2002). Alopecia areata nails grow slower than psoriatic nails. They are often indistinguishable from eczema nails, and in fact, both have a microscopical spongiotic dermatitis in common. Serum is in the spongiotic vesicles and becomes included into the nail; when it is very superficial it may break out and leave a depression, but when the origin is in the intermediate matrix the dried serum will remain in the nail and be the reason for the loss

When almost all nails are affected the so-called twenty-nail dystrophy is diagnosed (Samman, 1979). Even though this term does note denote a specific condition it is still widely used, particularly for 20-nail dystrophy of children (Horn and Odom, 1980, Baran

Psoriasis of the nails is an often neglected or overlooked disease as is evidenced by the most recent 100-page strong guidelines on psoriasis treatment (Nast et al, 2011), and it has a

The therapy of nail psoriasis is difficult, particularly that of isolated nail psoriasis as one usually hesitates to treat it systemically. In general, systemic treatment regimens that are effective in cutaneous psoriasis also improve nail lesions. There is a general lack of welldocumented studies and they are often not or difficult to compare (Jiaravuthisan et al, 2007) and few evidence-based treatments exist (Cassell and Kavanaugh, 2006). A standardized therapeutic approach does therefore not exist and preferred treatment regimens also differ between various countries. The treatment also depends on the nail structure involved, how severe the nail dystrophy is, whether there are extraungual lesions, the time needed for

Topical treatments are generally held not to be very effective. This has several simple reasons: Pits come from the depth of the nail pocket where the lesions are protected by the overlying proximal nail fold from being treated; lesions in the intermediate matrix are both hidden by the proximal nail fold and the nail plate; nail bed lesions are under the nail plate, which is a considerable obstacle to penetration of drugs. Ointments applied on finger nails may interfere with paper work. There are very few controlled studies on topical therapies. **Urea (**carbamide) is known for its keratolytic property. A paste containing 40% urea (Onyster®) softens fungus infected nails to a degree that it can be atraumatically removed; this may be a starting point for topical teatment. A 10% urea nail varnish was shown to improve the biophysical properties of the nail (Krüger et al, 2006). A 15% stable urea nail lacquer (Onypso®) is advertised as "the only specific topical treatment for nail psoriasis" as

it is claimed to reduce subungual hyperkeratosis. No controlled studies are available.

of nail transparence, nail thickening and brittleness.

subungual hyperkeratosis and later onycholysis as well as loss of nail transparency and shine (Hemmer et al, 1996).

a)

b)

Fig. 24. Onycholysis semilunaris (A) is characterized by its half-moon shape and clear border whereas psoriatic onycholysis has the typical appearance of an oil spot at its proximal margin (B).

When many or even all nails are affected the condition is called twenty nail dystrophy; this may, however, be a manifestation of ungual lichen planus, alopecia areata, eczema or psoriasis and the exact diagnosis often requires a histopathological examination of a nail biopsy.

subungual hyperkeratosis and later onycholysis as well as loss of nail transparency and

a)

b)

When many or even all nails are affected the condition is called twenty nail dystrophy; this may, however, be a manifestation of ungual lichen planus, alopecia areata, eczema or psoriasis and the exact diagnosis often requires a histopathological examination of a nail

Fig. 24. Onycholysis semilunaris (A) is characterized by its half-moon shape and clear border whereas psoriatic onycholysis has the typical appearance of an oil spot at its

shine (Hemmer et al, 1996).

proximal margin (B).

biopsy.

Irritant contact dermatitis was also estimated to mimic nail psoriasis (Takeuchi et al, 2010).

Alopecia areata is known to be associated with rough nails. The more extensive the alopecia areata is the more likely the patients also get nail changes. Most probably, isolated alopecia areata of the nails does exist (Tan et al, 2002, Nanda et al. 2002). Alopecia areata nails grow slower than psoriatic nails. They are often indistinguishable from eczema nails, and in fact, both have a microscopical spongiotic dermatitis in common. Serum is in the spongiotic vesicles and becomes included into the nail; when it is very superficial it may break out and leave a depression, but when the origin is in the intermediate matrix the dried serum will remain in the nail and be the reason for the loss of nail transparence, nail thickening and brittleness.

When almost all nails are affected the so-called twenty-nail dystrophy is diagnosed (Samman, 1979). Even though this term does note denote a specific condition it is still widely used, particularly for 20-nail dystrophy of children (Horn and Odom, 1980, Baran and Dawber, 1987).
