Cutaneous LCH can be the great pretender, mimicking a number of common dermatoses, and may represent the earliest sign of the disease [Caputo 1998]. As in childhood disease, a common manifestation is with scalp involvement. The typical lesions are small translucent papules, 1-2 mm in diameter, slightly raised and rose-yellow in colour; these lesions frequently show scaling or crusting, often leading to a misdiagnosis of seborrheic dermatitis. However, unlike seborrheic dermatitis, scalp LCH generally shows petechial haemorrhages which should help to differentiate it. Scaling and crusted lesions of the scalp simulate also tinea favosa. Pustules, which are commonly seen on the scalp, may be misdiagnosed as decalvant folliculitis or erosive pustular dermatosis of the scalp.
In adults, intertriginous involvement is often seen, the mainly affected skin folds being axillary, inguinal and anogenital. This presents with erythema and erosions, which are frequently misdiagnosed as eczema or psoriasis, but the lesions may be interpreted as a Candida infection or simply intertrigo; in these locations, Haley-Haley disease should also be considered. Pustular lesions involving the major cutaneous folds lead to the suspicion of hidradenitis or a new clinical entity within the spectrum of neutrophilic dermatoses, the so-called amicrobial pustulosis of the folds. A common presentation in men is with severe pruritus ani and ulceration around the anus; vulval irritation and ulceration is also not uncommon. Ulcerative lesions and ulcerated nodules located to the anogenital area may mimic several conditions, both inflammatory, notably pyoderma gangrenosum and Crohn’s disease, and neoplastic, particularly extramammary Paget’s disease and Bowen’s disease, as well as infectious and sexually transmitted diseases such as orificial tuberculosis and chancroid, respectively.
Generalised skin eruptions can look like guttate psoriasis with erythematous scaly patches covering the body, or prurigo nodularis with small hard papules and nodules, particularly on the trunk. Multiple erythematous papules involving mainly the trunk and extending to the extremities may also resemble lichen planus, especially the follicularis variant, or a lichenoid dermatitis of different causes; if vesicles are associated, the lesions can mimic varicella. When the cutaneous picture is polymorphic with papules, vesicles and necrotic-ulcerative lesions, acute pytiriasis lichenoides of Mucha-Habermann can be misdiagnosed. In addition to the more widespread disease, isolated erythematous papules may be the only manifestation with some patients only presenting with a single lesion and the diagnosis is only made when the lesion is removed for cosmetic reasons or due to concern about the possibility of a skin tumour. In fact, a single papule or nodule can suggest several neoplastic conditions, most notably cutaneous lymphomas, epithelial or adnexal tumours, sarcomas and metastases. Overlying involved lymph nodes or bone, LCH can present as ulceration or persistant sinus analogous to tuberculous scrofuloderma.
Gum involvement is a common presentation in the adult patient, almost always associated with alveolar bone involvement and loosening of the teeth. It is very important not to allow the dentist to extract the teeth as with treatment they will embed into the recovering alveolar bone. Nodular-ulcerative lesions involving the gums resemble the so-called strawberry gingivitis of Wegener’s granulomatosis, which is an unique form of gingival hyperplasia also mimicking that seen as possible side effect of oral cyclosporine.
Nail changes, include paronychia, onycholysis, subungueal hyperkeratosis and purpuric striae of the nail bed, suggesting a wide panel of conditions that affect the nails. Dark-brown striae similar to those drug-induced are also seen.
Cutaneous LCH has so many different manifestations that one needs a high level of suspicion and biopsy is essential. Although skin disease may be the primary presentation, one must investigate for systemic disease. (Grade D2 *)
* Grades of recommendation see here.