Sir,

The fingernails may present various changes in shape, size, color, and surface that might be inherent or due to various causes. Fingernail alterations due to finger abnormalities are uncommon.

Herein, we present the case of a 39-year-old male patient who was referred due to a digital fibroma located on the fifth right digit. Besides a paternal family history of cancer and diabetes, the patient had no other relevant medical history. During a physical examination, a localized onychopathy was observed on the nail of the right ring finger. The observed nail was characterized by flattening (Fig. 1a). The patient was asked to hold a pen, as if to write, to observe his writing grip, which appeared to promote flattening of the affected nail (Fig. 1b).

	Figure 1a: Flattening of the right ring fingernail.
	Figure 1b: Holding the pen or pencil, pressure on which can cause flattening of the affected nail.

Based on this onychologic finding, a diagnosis of platonychia of the right ring finger was made, secondary to the patient’s writing grip and pressure used when holding a pencil or pen to write.

Platonychia is defined as an abnormally flattened and widened nail, which may affect the toenails or fingernails [1,2]. Hyperkeratosis is typically observed in the central portion of the nail plate, and it may be a precursor lesion to koilonychia [3]. In previously reported cases involving the fingernails, a callosity at the level of the proximal fold of the affected finger has also been described [4]. An autosomal dominant inheritance pattern has been described in families presenting with multiple affected nails [1,5]. Platonychia has been associated with underlying conditions such as iron deficiency, vitamin C deficiency, onychophagia, Turnery syndrome, and Graves’ disease, among others [2,3]. Among the factors associated with toenail deformities secondary to digital deformities are foot shape and position, toe malformations, occupation, and footwear type, among others [4]. In 2008, a study of 77 patients with toe deformities-including overriding, crossing, and overlapping toes-reported that the most common nail deformity associated with these deformities was platonychia (48.1%), followed by onycholysis (41.5%), onychodystrophy (8.6%), and koilonychia (2.6%) [6]. In the fingernails, platonychia may be related to activities that produce repetitive trauma, such as habit tic deformity [7]. In the present case, it was associated with the patient’s writing grip, including the manner and pressure with which the pencil was held while writing [4]. It is important to teach children how to hold a pencil or pen correctly to prevent nail flattening, which has no consequence other than a cosmetic one.

REFERENCES

1.  National Library of Medicine, National Center for Biotechnology Information. Platonychia [Internet]. Available from:https://www.ncbi.nlm.nih.gov/medgen/340108

2.  James WD., Elston DM., Berger TG., Andrews G. Andrews’diseases of the skin:Clinical dermatology. 10^th ed. Saunders/Elsevier;2005. 786.

3.  Altmeyer P. Flat nail. In:Altmeyers Encyclopedia [Internet]. 2020. Available from:https://www.altmeyers.org/en/dermatology/flat-nail-124276#authors

4.  Chang DP. Platonychia. Five fingernail cases caused by chronic pressure with the pencil. Dermatología CMQ. 2010;8:127.

5.  Hamm H, Karl S, Bröcker EB. Isolated congenital nail dysplasia. Arch Dermatol. 20001;136:1239-43.

6.  Chang P, Porres P. 232 Deformidades de los artejos y alteraciones ungueales. Dermatología CMQ. 2008;6:232-40.

7.  Haneke E. Trastornos de autoagresión hacia las uñas. Dermatol Rev Mex [Internet]. 2013;53:225-34.