The diseases, which we may consider in the differential diagnosis with the papulosquamous pattern of SCLE are psoriasis and polymorphic light eruption.
3.3.1. Psoriasis vs papulosquamous SCLE Psoriasis is a chronic inflammatory disorder characterized by the presence of erythematous scaling plaques that in some cases can resemble SCLE. Differential features are a thicker scaling, with a silvery, micaceous appearance (Fig. 9) and a different distribution of psoriasis plaques that predominantly affect the elbows, knees, and the scalp, with no tendency to photodistribution.
In some cases skin folds and nails can be involved.
There is a genetical predisposition to develop psoriasis and therefore some of the relatives of affected patients may have the same disease.
Histology shows a characteristic hyperplasia (the so-called psoriasiform hyperplasia) with spongiform pustules and Munro microabscesses, that can be easily differentiated from SCLE.
3.3.2. Polymorphic light eruption vs papulosquamous SCLE Polymorphic light eruption represents the most common form of idiopathic photosensitivity disorder. It presents with a pruritic eruption with a variety of dermatologic expressions (erythematous papules, vescicles, or plaques) appearing on sun-exposed areas, mainly the extensor surfaces of the forearms and chest, less frequently also on the legs
and the face. The rash generally appears within a few hours, sometimes even 1-2 days after sun exposure and subsides spontaneously within 1-7 days provided that no further exposure occurs.
When appearing as erythematous plaques (Fig. 10), polymorphic light eruption may sometimes resemble early SCLE lesions, but can be differentiated because of the severe itch and the very precise timing with sun exposure, as polymorphic light eruption lesions erupt a few hours later and spontaneously resolve within some days without scarring or hypopigmentation.
Histological examination may not show a prominent epidermal involvement as in interface dermatitis, and when present, spongiosis may be an important differentiating feature.
The inflammatory infiltrate is mainly composed of lymphocytes, with variable amounts of neutrophils and eosinophils, and does not surround the appendages. Moreover, dermal edema may be prominent (Stratigos et al., 2002; Tutrone et al., 2003).
3.4. Differential diagnosis of annular-polycyclic SCLE
3.4.1. Superficial gyrate erythema vs annular-polycyclic SCLE Superficial gyrate erythema is considered as a poli-aetiological reaction-pattern with a typical expression and running a chronic course. It may present with elevated urticarial plaques with centrifugal spreading and central resolution that form arched, ring-shaped or polycyclic patches involving the trunk and the proximal limbs resembling SCLE.
Differential features are the asymmetric involvement of the trunk without photodistribution, the rapid extension of the rings, which may become larger than it can possibly be observed in SCLE, and the spontanous clearing without hypopigmen-tation or telangiectases. Moreover, a characteristic scaling at the trailing edge of the advancing border may be observed (Fig. 11).
Histological examination reveals spongiosis with microvesciculation, focal parakeratosis, and a mild perivascular lymphohistiocytic inflammatory infiltrate, with sparing of the appendages (Lever and Schaumburg-Lever, 1990).
3.4.2. Tinea corporis vs annular-polycyclic SCLE
Dermatophytes are keratinophilic fungi that can produce different patterns of superficial infection of the glabrous skin. A non-inflammatory pattern, tinea circinata, presents with annular lesions with an active erythematous scaling border and central clearing. Contiguous annular lesions may merge to form polycyclic plaques that can be confused with SCLE, but tinea corporis is generally asymmetric and non-photodistributed.
Moreover, KOH examination of the scales obtained by scraping from the active border can show the presence of hyphae, and the culture on appropriate media can allow for the identification of the causative microorganism.
4. Chronic cutaneous lupus erythematosus
Among the cutaneous manifestations of LE, those comprised under the category of CCLE are the most frequently observed. The face and the scalp are the most commonly affected areas (localized CCLE) but any other part of the body below the neck can be involved as well (generalized CCLE).
At onset, CCLE appears as a sharply demarcated, slightly raised, erythematous lesion. Hyper-keratosis gradually develops and therefore the surface becomes rough at first, and then scaly.
Sometimes hyperkeratosis may be predominant at the follicular orifices, which appear dilated and filled with a keratin plug. The scales may then become thick, adherent, and when they are removed, the follicular plugs attached to the underside form characteristic horny spikes, the so-called 'carpet tack' appearance.
CCLE lesions gradually become infiltrated and extend peripherally with an active erythemato-squamous border, while partially resolving in the central area, with the development of scleroatro-phy, telangiectases, hypo- or hyperpigmentation and cicatricial alopecia.
In larger plaques, the peripheral extension may become irregular, with only isolated arciform segments of the active border.
With time, inflammation subsides leaving only scleroatrophic and dyschromic residues that cause permanent disfiguring results.
Various diseases have to be considered in differential diagnosis according to the different stages of the evolution of the CCLE. For this reason, we have separated early, fully developed, and late CCLE lesions, and within early lesions we have arbitrarily identified two clinical patterns: scaling and non-scaling early CCLE.
The non-scaling pattern of early CCLE lesion presents as an erythematous plaque, sharply demarcated, with minimal scaling. Lupus tumidus, in which the papular component is predominant, can be considered as an extreme of the spectrum of the non-scaling pattern of CCLE manifestations.
The scaling pattern of early CCLE lesion presents as an erythematous plaque with prominent follicular hyperkeratosis and scaling. A hyper-trophic variant of CCLE may represent one extreme of the spectrum of the scaling pattern.
Fully developed CCLE lesion: annular lesion with an active border with erythema, infiltration and scaling and a central area with sclerosis, atrophy, and telangiectases.
Late CCLE lesions: scleroatrophic patches with telangiectases and only limited areas of residual inflammation within the patch and in the periphery, where they may form an incomplete active margin.
4.2. Clinical background
CCLE can be the isolated expression of a localized cutaneous disease but it can also occur in patients with SLE.
4.3. Differential diagnosis of early CCLE, non-scaling pattern
The diseases, which we may consider in differential diagnosis with the non-scaling pattern of early CCLE, are polymorphic light eruption, Jessner's benign lymphocytic infiltration of the skin, lympho-cytoma cutis, granuloma faciale, pernio (chilblain), and lupus pernio (sarcoidosis). The same diseases may also be considered in the differential diagnosis with tumid LE.
4.3.1. Polymorphic light eruption vs early CCLE, non-scaling pattern Polymorphic light eruption has already been mentioned in Section 3.3.2.
When it presents as an erythematous papular or plaque eruption involving the face, it should be considered in the differential diagnosis with CCLE, and above all, tumid LE.
Distinguishing clinical features are the presence of itching, which is often severe and the precise correlation with the sun exposure and the quick resolution within a few days, while CCLE and tumid LE do not itch and the latency before the eruption is longer, days or even weeks after sun exposure, and the lesions tend to be persistent.
Histology shows the following distinguishing features: there is no epidermal involvement in the papular variants of polymorphic light eruption, there is edema in the papillary dermis, the inflammatory infiltrate may contain variable amounts of neutrophils, and does not involve the appendages as in CCLE.
4.3.2. Jessner's benign lymphocytic infiltration of the skin vs early CCLE, non-scaling pattern
Jessner and Kanof (1953) first described this disease which is characterized by the occurrence of asymptomatic, erythematous papules and plaques, with a smooth surface, that tend to a peripheral extension and central resolution evolving to annular or horseshoe-like configuration, occurring mainly on the face (Fig. 12) and less often on the trunk. Jessner's lesions tend to be persistent or may have a relapsing course, may be induced or aggravated by sun exposure, but most of the patients have active lesions during wintertime and on non-exposed areas of the trunk.
Jessner's lymphocytic infiltration may closely resemble tumid LE, and in this respect, some authors suggest that it should not be considered as a separate entity but rather a variant of CCLE or, in some cases, of polymorphic light eruption.
Jessner's lymphocytic infiltration is characterized by a coat-sleeve perivascular lymphocytic infiltrate as the only histologic feature (Massi, 1995). CCLE may, therefore, be differentiated by the presence of
epidermal involvement and patchy lymphocytic infiltrates in the superficial dermis below the dermo-epidermal junction and around hair follicles while tumid LE may be distinguished by the presence of minimal signs of epidermal involvement and the abundant mucin deposition. DIF is negative in Jessner's lymphocytic infiltration and recently immunohistochemical analysis has revealed a predominance of CD8+ T lymphocytes in the inflammatory infiltrate (Poenitz et al., 2003).
4.3.3. Lymphocytoma cutis vs early CCLE, non-scaling pattern
Lymphocytoma cutis is the prototype of cutaneous B-cell pseudolymphomas. It appears as one or several erythematous papules or plaques, with a smooth surface (Fig. 13). The majority of lymphocytoma cutis involve exposed areas of the head and the neck, and in the earlier stages of development, when the papular or plaque component is not yet fully expressed, it can be considered in the differential diagnosis with early CCLE, while in later stages lymphocytoma cutis lesions can more closely resemble tumid LE.
Clinical diagnosis is impossible and therefore the differentiation requires the histologic examination
Figure 13. Lymphocytoma cutis: smooth, bright red papule on the tip of the nose.
of the lesions. Lymphocytoma cutis presents with a normal epidermis, a grenz-zone of uninvolved superficial dermis, and an underlying dense infiltrate extending throughout the reticular dermis in a 'top-heavy' pattern, composed of a mixed infiltrate with a majority of B-lymphocytes, and a variable amount of histocytes, plasma cells, and occasional eosinophils. Germinal centers are often present, surrounded by plasma cells (Massi, 1995).
4.3.4. Granuloma faciale vs early CCLE, non-scaling pattern
This is a rare form of localized chronic fibro-sing vasculitis of the skin. It generally begins as a solitary, well-circumscribed erythematous papule (Fig. 14), and at this stage a biopsy is necessary for the differential diagnosis with early CCLE. Eventually, the initial purple color may shift to reddish-brown (due to hemosiderin deposition), and the slightly raised smooth surface develops characteristic prominent follicular orifices, but never hyper-keratosis or follicular plugging as in CCLE, therefore allowing for a high degree of clinical suspicion.
The main histologic features of granuloma faciale are the absence of epidermal involvement, a grenz-zone of uninvolved superficial dermis, a leu-kocytoclastic vasculitis with nuclear dust and a mixed dermal infiltrate with prominent neutrophils and eosinophils.
DIF studies (Zirwas et al., 2003) have given conflicting results as some authors have reported the presence of immunoglobulin deposits in the blood vessel walls, while others have not confirmed this finding. Moreover, the deposition of IgA, IgG, IgM, and C3 along the dermo-epidermal junction with a granular pattern and a negative fluorescence of the blood vessel walls, may closely mimic the DIF pattern found in LE.
4.3.5. Pernio vs early CCLE, non-scaling pattern
Pernio or chilblain is a reaction pattern to cold exposure in damp climates, presenting as vivid red to purple plaques, warm to the touch, accompanied by itching and at times also soreness and pain. They are most commonly localized on the dorsal surface of the fingers and in other acral areas, and tend to persist throughout the cold season.
The face may be affected, and when plaques are localized in the malar area (Fig. 15) and itching is not prominent, a suspicion of CCLE may arise. Generally other lesions may be present in areas unusual for CCLE, but in some cases a biopsy will be necessary for differential diagnosis.
Peculiar histologic features are the presence of spongiosis, necrotic keratinocytes, an intense papillary dermal edema, a mononuclear inflammatory infiltrate with a prevalence of T cell and with a per-ieccrine reinforcement, and sometimes thrombosis
of dermal papillae capillaries (Crowson and Magro, 1997; Cribier et al., 2001).
Some CCLE patients may develop chilblain lesions on the extremities that evolve to form characteristic discoid LE (DLE) plaques, with a typical clinical appearance and a diagnostic pathology, for which the term 'chilblain lupus' or 'perniotic LE' has been proposed. This phenomenon might represent a peculiar form of a Koebner reaction triggered by the chilblains (Millard and Rowell, 1978).
4.3.6. Lupus pernio vs early CCLE, non-scaling pattern
Lupus pernio is a peculiar pattern of cutaneous involvement in patients with sarcoidosis with a chronic, fibrotic involvement of the lungs and other systems. It presents with persistent, violaceous plaques on the nose, cheeks, and ears that must be differentiated from CCLE (Fig. 16). On clinical groundlupus pernio tends to have a smooth, glistening surface without scaling, and follicular orifices may be prominent but without follicular plugging. Histology shows the absence of epidermal involvement but the most important differentiating feature is the presence of non-caseating epithelioid-cell granulomas. Eventually, some biological markers like elevated levels of serum-angiotensin converting enzyme, lysozyme, beta 2 microglobulin, and disturbed calcium metabolism (hypercalcemia and hypercalciuria) may be helpful for the diagnosis of sarcoidosis.
4.4. Differential diagnosis of early CCLE, scaling pattern
The diseases, which we may consider in differential diagnosis with the scaling pattern of early CCLE are actinic keratoses, seborrheic dermatitis, tinea faciei, psoriasis, and lichen ruber planus.
4.4.1. Actinic keratoses vs early CCLE, scaling pattern
Actinic keratoses are the most frequent precancer-ous cutaneous lesions. They may be found on the exposed areas, most frequently on the face and the bald portion of the scalp, but also on the trunk and arms in fair-skinned individuals. They appear as areas of macular erythema with an overlying adherent scale. Scaling may be minimal, best appreciated by touch, while on the other hand, in some cases of hypertrophic actinic keratoses the formation of a cutaneous horn may be seen.
Actinic keratoses may be similar to early CCLE but are slower in their evolution, rougher to the touch, and the scales are very difficult to detach, with no follicular plugging.
Moreover, they are always observed within areas of photodamaged skin in individuals older than the average CCLE patient.
Histology shows dysplastic keratinocytes, dys-keratosis, loss of cell polarity, especially in the lower epidermis, with sparing of the adnexa.
4.4.2. Seborrheic dermatitis vs early CCLE, scaling pattern
Seborrheic dermatitis may be considered in differential diagnosis with early CCLE when it presents as erythematous scaling patches on the scalp or with atypical features (Fig. 17).
The scales in seborrheic dermatitis have a greasy appearance, a yellowish color, and may be easily detached by scraping while CCLE tends to develop dry, whitish, adherent scales with a tendency to follicular plugging, and therefore a clinical differentiation is generally possible.
4.4.3. Psoriasis vs early CCLE, scaling pattern
As in the case of seborrheic dermatitis, psoriasis can create some suspicion of CCLE when it presents with an isolated localization on the scalp. Psoriasis also frequently involves the peripheral areas of the scalp extending toward the forehead
and the retroauricular folds. Moreover, the scales are silvery-white, easily detached by gentle scraping, and uniformly distributed over the plaque surface, where they may sometimes form a thick layer, and leaving only a peripheral erythematosus, raised border.
4.4.4. Tinea faciei vs early CCLE, scaling pattern
Dermatophytic infection of the face has been referred to as tinea faciei, and may take on unexpected forms, particularly in the adult or in immuno-compromised patients, thus resembling other diseases, most frequently DLE (Alteras et al., 1988).
It may appear as non-symmetric erythematous plaques, with variable scaling (Fig. 18) and sometimes follicular plugging and a suspicion of DLE may arise when the nose or the malar areas are involved.
For the differential diagnosis, KOH examination of cutaneous scales may be employed, allowing for the detection of the hyphae. Moreover, a precise identification of the causative dermatophyte can be made on appropriate culture media.
4.4.5. Lichen ruber planus vs early CCLE, scaling pattern
Lichen ruber planus is characterized by the eruption of tiny, flat-topped, polygonal, violaceous papules, with variable hyperkeratosis going from delicate white lines (Wickham's striae) to a verrucous appearance. The papules are generally symmetrically distributed over the flexor surfaces of the forearms and wrists but may be more widespread to involve the trunk, the genital and oral mucosa, and sometimes the scalp.
The distribution of the rash and the presence of itching are characteristic differentiating features from CCLE, but occasionally, isolated plaques of lichen ruber planus may induce a suspicion of LE.
Distinguishing histologic features of lichen rub-er planus are the presence of a band-like inflammatory infiltrate below the dermo-epidermal junction, a 'saw-toothed contour' of the rete ridges, and colloid bodies, which are more numerous than in CCLE and may be aggregated.
DIF may show a fibrillar or band-like pattern of fibrin deposition along the dermo-epidermal junction, while colloid bodies demonstrate IgM staining and less frequently IgA, IgG and C3 staining (Nieboer, 1987).
Nonetheless, rare patients with intermediate features or with the simultanous occurrence of CCLE and lichen ruber planus have been described as lichen-lupus overlap syndrome.
4.5. Differential diagnosis of fully developed CCLE lesions
Fully developed CCLE lesions have a unique appearance and can hardly be confused with other diseases. According to Sontheimer and Provost (1995), "Discoid-shaped skin lesions that have erythema and hyperpigmentation at their active borders, and depigmentation, telangieactasia, and atrophy at the centres are very unlikely to result from dermatologic disorders other than cutaneous LE''.
The diseases, which can be considered in differential diagnosis with late CCLE are lichen ruber planus, lupus vulgaris, and other granulomatous infectious diseases.
4.6.1. Lichen ruber planus vs late CCLE The involvement of the scalp is very frequent in a variant of lichen ruber planus called lichen plano-pilaris, and leads to the development of a cicatri-cial alopecia that has to be differentiated from late CCLE of the scalp.
Initially small erythematous follicular papules may be observed, with little scaling stuffing the in-fundibula and progressing to form follicular horny plugs. Soon scarring takes place leaving a white, smooth alopecic area (Fig. 19), while follicular plugging and inflammatory papules remain visible only at the periphery (Fig. 20).
On clinical grounds it can be differentiated from late CCLE lesions because of the absence of telan-giectases, hyperpigmentation, and of residual areas of inflammatory activity and scaling at the margins of the patch. During active phases, the hairs surrounding the alopecic area can be easily pulled out with a minimal traction, even if the underlying skin is apparently normal, while in CCLE this can happen only within the inflamed area.
Moreover, late CCLE lesions are generally completely devoid of hairs while in lichen planus sparse isolated hairs may still be observed within the area of alopecia.
Some peculiar histologic features allow for the differentiation from CCLE: the inflammatory infiltrate involves predominantly the hair follicles and the surrounding dermis in lichen planus, and in alopecic areas, a band-like fibrotic thickening of the papillary
dermis may be observed, with fibrotic tracts at the sites of destroyed hair follicles (Annessi et al., 1999).
The lupus band test is positive in the majority of cases of late CCLE of the scalp (Fabbri et al., 2004) and therefore DIF is particularly helpful in the differentiation from alopecia of lichen plano-pilaris (see Section 4.4.5).
4.6.2. Lupus vulgaris vs late CCLE Among the various forms of cutaneous tuberculosis, lupus vulgaris should be considered in differential diagnosis with late CCLE. It can be observed in patients with a considerable degree of immunity against mycobacteria, and runs a chronic, progressive course.
It begins as a small erythematous plaque of soft consistency, generally involving the head and neck, most frequently around the nose. The plaques slowly extend peripherally and may develop variable amounts of scaling and irregular scarring and ulcerations. At the edge of the plaque, small nodules may be observed, with a characteristic 'apple jelly' color; when gently probed, they result of a soft consistence, and the overlying skin can be easily torn-up.
In untreated cases, the involvement and the destruction of the cartilages of the nose and the ear may lead to deformity and mutilation, hence the term 'lupus'.
Differentiating clinical features are the development of ulcerations and crusts, which are rather unusual in CCLE, and the presence of the characteristic 'apple-jelly' nodules.
Histology shows the presence of epithelioid cell granulomas with Langhans giant cells and variable caseation, surrounded by an infiltrate of histiocytes and lymphocytes and variable amounts of fibrosis. Moreover, mycobacteria can be isolated from a biopsy specimen by culture or identified by poly-merase chain reaction.
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