Psoriasis is an inflammatory skin disease with a prevalence of approximately 2% worldwide, psoriasis vulgaris (PV) is the most common variant of it. The lesion of PV is usually characteristic, so the diagnosis is mainly made clinically. Sometimes PV may be mistaken for other erythematosquamous diseases, such as eczema, seborrheic dermatitis, pityriasis rosea and pityriasis rubra pilaris, resulting in delayed appropriate treatment, so skin biopsy with histological examination to confirm the diagnosis is needed. In vivo reflectance confocal microscopy (RCM) is a novel real-time imaging technique that may facilitate the diagnosis of some skin diseases. We describe 50 patients with stable PV and 55 patients with other skin diseases imaged using RCM, the sensitivity and specificity of Munro’s microabscess detected by RCM in the diagnosis of PV were determined.
The study group includes 50 patients with stable PV, the control group includes 24 patients with eczema, 15 patients with pityriasis rosea, 13 patients with seborrheic dermatitis and three patients with pityriasis rubra pilaris. Most of the patients were diagnosed only by clinical findings, five patients with PV, four patients with eczema, two patients with seborrheic dermatitis and three patients with pityriasis rubra pilaris were diagnosed by histological examination, none of the patients was under systemic or topical treatment, at least 1 month prior to the beginning of the study. All the patients were recruited during the period from October 2010 to March 2011 from the Department of Dermatology, Affiliated Hospital of XuZhou Medical College, China. All the patients were imaged using RCM (Vivascope 1500; Lucid, Rochester, NY, USA). In the first three patients with PV, a skin biopsy was taken in order to correlate the RCM images with histological findings of just the same lesion that was examined by RCM.
Infiltrating leukocytes within the horny layer (Munro’s microabscess) can be easily demonstrated by RCM, they are highly refractile and twinkling particles compared to the surrounding keratinized background (Fig. 1). In the first three patients with PV, histological examination also demonstrated Munro’s microabscess in the same lesion that was examined by RCM (Fig. 2). Munro’s microabscesses were found in 45 (90.0%) patients in the study group and two (3.6%) patients with eczema in the control group. The positivity rate of Munro’s microabscess in the study group was significantly higher than that in the control group (P < 0.001). The diagnostic sensitivity of Munro’s microabscess detected by RCM in the diagnosis of PV was 90.0% and the diagnostic specificity 96.4%.
Other histological presentations of PV such as parakeratosis and the tortuosity and extension of dermal papilla blood capillary can also be demonstrated by RCM. Parakeratosis can be seen as numerous, highly refractile nucleated structures (Fig. 2a), which was found in 46 patients in the study group and 23 patients in the control group. Tortuous and dilated blood capillaries can also be seen within the upper dermis (Fig. 2b), which was found in 35 patients in the study group and 15 patients in the control group.
The histological presentations of PV comprises parakeratosis, absence or diminished granular layer, acanthosis, thinning of the suprapapillary plate, elongation of the dermal papillae, trafficking of inflammatory cells through the epidermis (microabscesses of Munro and microabscesses of Kogoj), and tortuous, dilated capillaries in the reticular and papillary epidermis.
In contrast to standard histopathology for which biopsy specimens are needed, RCM is a non-invasive, real-time and prompt technique. Several recent publications have documented the use of RCM in the diagnosis of different skin disorders, including melanoma,1 basal cell carcinoma,2 actinic keratoses3 and allergic contact dermatitis.4 In 1999, Gonzalez et al.5 showed that well-known histological features of psoriasis could be identified using RCM. Further correlations between RCM and routine histology were demonstrated by Ardigo et al.6 in 2009.
Microabscess of Munro is highly specific for the diagnosis of psoriasis, so we designed this study to investigate the sensitivity and specificity of Munro’s microabscess detected by RCM in the diagnosis of PV. The results demonstrated that the sensitivity of Munro’s microabscess detected by RCM in the diagnosis of PV was 90.0% and specificity 96.4%. Our results suggest that RCM may be considered a promising tool in the diagnosis and differential diagnosis of PV.
There are some structures other than Munro’s microabscess showing the same refractile and twinkling properties in the horny layer, such as pustule in the lesion of subcorneal pustular dermatosis, and pustule in the lesion of other skin diseases caused by secondary bacterial infection. RCM finding for Pautrier’s microabscess and pseudo-Pautrier’s microabscess is also similar to that of Munro’s microabscess, but the cells in which are smaller, not twinkling and less refractile.
In summary, our results suggest that Munro’s microabscess is the most important finding in the diagnosis and differential diagnosis of PV using RCM, but the diagnosis cannot be established only by the presence of Munro’s microabscess, other findings by RCM such as parakeratosis and the tortuosity and extension of dermal papilla blood capillaries are helpful, and clinical manifestations are also very important in the diagnosis of PV.