Nail clipping may not be sufficient to corroborate the diagnosis of psoriasis

Nail clipping may not be sufficient to corroborate the diagnosis of psoriasis. Nail clipping is an easy and painless biopsy technique that does not require specific training or anaesthesia and does not cause onychodystrophy. By cutting the free edge of the most affected nail with a straight nipper, a 2 × 5 mm sample of the onycholytic nail plate is obtained, until its most proximal part. The sample should preferably be submitted in a dry container or saline solution. There are several options for softening the nail plate specimens in the pathology laboratory. This includes 4% phenol, 10%–20% sodium or potassium hydroxide, 10% aqueous solution of Tween 40 or methacrylate. Histological sections are stained with haematoxylin–eosin and periodic acid-Schiff immunohistochemical (PAS) (for fungal search).1, 2 In nail disorders, clinical signs are not only limited but also shared by different diseases. Subungual hyperkeratosis and onycholysis, for example, can be manifestations of nail lichen planus, onychomycosis and nail psoriasis.3 As about 1%–5% of patients with psoriasis have isolated nail involvement, nail biopsy is necessary for diagnosis, therapeutic planning and prognosis estimation.3 Finding neutrophils and parakeratosis within the nail plate, especially if associated with a PAS-negative reaction for fungi, supports the diagnosis of psoriasis.2 Neutrophils collections seem to be more common in onychomycosis and continuous parakeratosis is more frequent in psoriasis.4 Other findings described in psoriasis are subungual hyperkeratosis and serous lakes.2 We have previously reported a study of nine patients with nail psoriasis, confirmed by histopathological examination of the nail bed. Nail plate samples were also analysed. Three patients (33%) presented significant clinical changes suggestive of psoriasis involving all 10 fingernails (Figure 1) and histopathological findings of the nail plates consistent with psoriasis.5 The histopathological changes found in the nail plate were papillomatosis, suprapapillary intracorneal serous exudate, parakeratosis and intracorneal neutrophils, as well as absence of fungi on PAS staining (Figure 2). The other six patients revealed only nail plate surface irregularity and hyperkeratosis, with foci of parakeratosis in some of them. It is likely that the more pronounced the clinical signs, the greater the likelihood of histological findings in the nail plate. Accordingly, it is important to alert about the potential limitation of nail clipping for the diagnosis of psoriasis. The histopathological analysis of the underlying nail bed was crucial for the diagnosis of psoriasis in those 6 (67%) patients. Parakeratosis, focal thinning of the granular layer and of the suprapapillary epidermis, intra- or subcorneal neutrophils collections, regular epidermal hyperplasia and hypervascularization of the dermal papillae were found (Figure 2).5 Therefore, evaluating only a specimen obtained by nail clipping would not be sufficient for psoriasis diagnosis in most of the patients. Dermatologists often avoid nail bed/matrix biopsies due to the risk of nail dystrophy. In addition, the lack of prior training in nail surgery is commonly an obstacle. However, the sensitivity of the clipping method is limited and histopathological psoriasis features may not be significant in the distal nail plate. In sum, in this small sample, the positive rate of nail clipping for psoriasis diagnosis was low. Despite being a useful tool in daily practice, in inconclusive cases, sampling of the subungual soft tissues is necessary to improve diagnostic accuracy. New studies with a larger sample size may demonstrate the true sensitivity of the nail clipping method for the diagnosis of psoriasis. This work was carried out with support from the Coordination for the Improvement of Higher Education Personnel—Brazil (CAPES)—funding code 001. The authors declare no conflict of interest. Manuscript reviewed and approved CAAE: 55474521.1.0000.5404. Informed consent was obtained from the patient reported in this manuscript. The data that support the findings of this study are available from the corresponding author upon reasonable request.