Dermatologic aspects of onychophagia

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Onychophagia is a chronic disorder characterized by chronic repetitive traumatization of the nail plates of the fingers and toes by placing them in the mouth with further biting and chewing [1, 2, 3, 4]. Although other terms have been proposed to describe this disorder, such as “Onychodaxia” (Greek “daxia” - to bite) [5], it is the term “Onychophagia” that is the established universally recognized definition in the medical community. 
Epidemiologic assessment of the prevalence of onychophagia is a major challenge, as people suffering from this disorder rarely seek medical care. Despite this, according to data obtained in a number of studies, today this disorder affects about 20-30% of the world's population [2, 6, 7]. The age of patients plays an important role in assessing the prevalence of onychophagia. It has been noted that children under three years of age practically do not suffer from this disorder, while 45% of cases fall within the age period of 10 years and older [8]. In some patients, the habit persists or appears much later in adulthood [8, 9].

The etiopathogenesis of onychophagia remains unclear. Onychophagia is believed to be a heterogeneous disease, with both genetic and environmental factors playing a role in its development. A clear family history of onychophagia has been reported in several studies, which involved both siblings and parents of patients [13, 14]. Also in a study by Ooki, S. it was shown that the habit of nail biting was genetically related and was present in 50% of twin pairs [13]. External environmental factors also influence the development of onychophagia. According to studies, the emergence of nail biting and nail biting habit in children is associated with imitation of behavior and imitation of older family members [12]. 
Onychophagia is the cause of the development of many comorbid disorders. Speaking of psychiatric pathology, onychophagia is often associated with onychophagia, trichotillomania, cheilophagia, cheek biting habit (a variant of dermatophagia) and neurotic excoriations [17]. Among the most common dental disorders in patients with onychophagia are the development of clinical crowding and rotation of teeth, formation of malocclusion and gingivitis [18], although the most serious problem is infection of the patient's oral cavity with bacteria of the genus Enterobacteriaceae.  [15]. 

Despite the marked heterogeneity of onychophagy and the variety of associated disorders, the dermatologist's examination plays a central role in both the diagnosis and the correct routing of the patient. Moreover, it is the dermatologist who corrects the main consequence of the disease, the nail lesions, which in turn reduces the social maladjustment of patients and may in some situations increase the chances of maintaining a relatively durable remission.

Lesions of the nail apparatus in onychophagia

The nail apparatus is the main target of lesions in onychophagia. Practically all structures of the nail apparatus are involved in the pathological process, starting from the nail plate itself, ending with the nail bed and the adjacent skin. Usually, several nail plates on both hands are symmetrically involved in the pathologic process [21] (Figure 1).

Fig. 1(a,b). Symmetrical lesions of the nail plates of the I and II fingers of both hands in a patient with onychophagia.

The general appearance of the nails in onychophagia is a shortening and overall reduction of the nail plates [22, 23] (Figure 2).

 The nails appear dehydrated and dull. In severe cases, subtotal or total absence of nails involved in the pathologic process is noted [24, 25].  

Fig. 2. Shortening and overall reduction of nail plates in a patient with onychophagia

The clinical picture of nail lesions in onychophagia is dominated by nail dystrophies of predominantly atrophic type. The leading type of dystrophy in onychophagia is onychoschisis, i.e., delamination of the free edge of the nail [18]. Given that not only the free edge but also the entire nail plate is subjected to mechanical irritation in the form of bites, delamination can occur along the entire length of the nail, which is called lamellar onychoschisis [16] (Figure 3). 

Fig. 3: Lamellar onychoschisis in patients on the free edge (a) and central part (b,c) of nail plates

Ventral nail pterygium (syn. Pterygium inversum unguis), characterized by the growth of hyponychium to the ventral layer of the nail and its gradual atrophy towards the matrix, is less common [23, 24, 25]. This clinical manifestation of onychophagia is the most severe, since in most cases it is irreversible. Also common non-specific nail lesions in onychophagia are transverse and longitudinal furrows, resulting from both chronic traumatization and regular contact with an aggressive environment (saliva) [27]. 
Changes in nail color are also characteristic of patients with onychophagia. Prolonged chronic traumatization of the nail apparatus leads to stimulation of the melanocyte population in the nail matrix by melanocytic activation (more frequent) and melanocytic hyperplasia (less frequent), which is clinically manifested by the development of longitudinal melanonychia [18, 19, 24, 25]. Depending on the type of melanocyte activation we get a different clinical picture of melanonychia: if melanonychia was formed due to melanocytic hyperplasia, the color of the nail plate will change to brown-black, if due to melanocytic activation, the color of the nail plate change will be gray [24]. 
Chronic traumatic action on the nail matrix also affects the degree of onychocyte maturation and differentiation, which is clinically manifested by the development of longitudinal (less often) and/or pitting (more often) true leukonychia in patients with onychophagia [18, 19].

The pathologic process in onychophagia also often involves the nail bed. Patients have single or multiple longitudinal hemorrhages mainly in the distal part of the nail bed and in the central and proximal parts in severe cases [18, 19, 21] (Figure 4). 

Fig. 4. Multiple pronounced longitudinal furrows, lamellar onychochisis and longitudinal hemorrhages of the nail bed in a patient with onychophagia.

Clinical evaluation of the cuticle and near nail shafts is also an important diagnostic feature. In onychophagia, the cuticle is most often uneven, torn, or absent, which is most often associated with other compulsive disorders (26,27,28). Abrupt thickening and layering of the cuticle as a response to repetitive mechanical stimuli may also be noted. One clear sign of onychophagia is the presence of periungual skin lesions at various stages of healing [28] (Figure 5). 

Fig.5. Cuticle and skin lesions of periungual nail rollers in onychophagia: a - skin lesions of the proximal nail rollers; b - torn and hypertrophied cuticle

The nail well, as a derived structure of the nail apparatus, also responds to chronic mechanical irritation. Macrolunula, a condition in which there is marked enlargement of the nail well, is a response of the nail apparatus to chronic traumatization in patients with onychophagia [21] (Figure 6). 

The described changes of the nail apparatus in onychophagia are summarized in Table 1.
Table 1. Lesions of the nail apparatus in onychophagia

Nail dystrophies	Nail discoloration	Nail bed	Nail shaft skin and cuticle	Nail bed
Onychoschisis	Melanonychia	Longitudinal hemorrhages	Ripped cuticle or no cuticle	Macrolunula
Longitudinal and transverse furrows	Leukonychia		Cuticle thickening
Ventral pterygum			Various skin injuries at different stages of healing

Complications of onychophagia
The main complication of onychophagia is acute and chronic paronychia [16] (Figure 7). In severe advanced cases of the disease, patients with onychophagia may develop osteomyelitis of the bones of the distal phalanges of the fingers [16, 29, 30]. Patients with onychophagia have also been found to be more prone to develop viral infections in the affected skin areas. Patients with onychophagia often have frequent manifestations of herpetic infection (herpes panariculosis) and human papillomavirus (subnail viral warts ) [16, 30, 31]. Rare cases of intraosseous epidermal cysts have also been described in patients with onychophagia [31, 32]. 

Fig. 7: Paronychia in patients with onychophagia: a - mild course; b,c - severe chronic process

Differential diagnosis
An important point in the diagnosis of onychophagia is the assessment of the patient's general condition. Attention should be paid to the patient's behavior during clinical examination: whether the patient is active or indifferent, whether he does not commit an act of autodestruction of nails during admission, etc. All 20 nail plates, all skin, especially the scalp and anterior teeth, should be examined for signs of mechanical self-harm. Other family members' nail plates should also be examined if possible.
If we are talking about adult patients, an important role in the diagnosis of onychophagia plays an important role in the collection of anamnesis. It is necessary to clarify from the patient his occupation and profession, as well as hobbies and possible household habits. An important question is the patient's attitude to his condition, how he takes care of his nails, how he tries to restore their healthy appearance. 
Despite the relative paucity of the clinical picture, onychophagia may be similar to some infectious diseases and chronic dermatoses (Table 2). 
Table 2. Differential diagnosis of onychophagia

Disease/pathologic condition	Diagnostic criteria
Mechanical trauma	History data
Nail mycosis	Analysis of nail plates for the presence of parasitic fungi
Melanocytic nevus/melanoma of the nail apparatus	History data (including negative Getchinson's symptom); Results of dermatoscopic examination; Biopsy
Lozier-Hanziker syndrome	Presence of pigmentation foci on oral mucosa and lips
Nail psoriasis	Anamnesis data;  Presence of symptoms specific to nail psoriasis (Rosenau and Keuning_Hassenflug symptom);  Presence of psoriasis foci on the skin Nail lesions in CRPS Anamnesis data;
Nail lesions in CRPS	Anamnesis data;  Presence of foci of KPL on the skin; Presence of onychorexis as the leading type of dystrophy in KPL

Onychophagia should be differentiated with mechanical trauma, nail psoriasis [32], nail lesions in red flat lichen planus (RPL) [33], nail mycosis, melanocytic nevus and nail melanoma [34], as well as Logier-Hanziker syndrome [34, 35, 36], vasculitis [37], and systemic connective tissue diseases [38]. Signs of differential diagnosis are summarized in Table 2. 
Therapy of onychophagia 
To date, there are no effective treatments for onychophagia. The psychological basis of the disease is obvious, which implies that the main role in the therapy of this disorder should be played by family/child psychologists, psychotherapists, and psychiatrists. 

At the same time, the clinical picture of the disease manifests itself most clearly on the nail plates and the therapeutic options of dermatologists in helping patients with onychophagia are very limited. 
Dermatologists may recommend the use of protective gloves, expensive professional nail care, and bitter-tasting nail polish to help patients with onychophagia, but all of these recommendations usually have an unstable effect [39]. 
Of particular interest in the therapy of onychophagia is the use of acetylcysteine-based preparations. In a randomized double-blind placebo-controlled clinical pilot study conducted by Ghanizadeh [40] it was shown that administration of acetylcysteine preparations at a dose of 800mg per day in 42 children and adolescents gave statistically significant improvement in general condition and nail growth compared to placebo. In Berk's study [41] it was shown that administration of acetylcysteine preparations at a dose of 1000mg 2 times a day resulted in complete disappearance of onychophagia symptoms in three described clinical cases. 

Our own observations show that the use of acetylcysteine in a dosage of 800mg per day for 3 months leads to almost complete disappearance of onychophagia symptoms in patients regardless of age and sex. Even in case of remission of the pathological process, this course is recommended to be repeated after a 1-month break. Further tactics of patient management depends on the specific clinical situation and the patient's condition.Administration of acetylcysteine preparations and monitoring of dermatologic status should be carried out in parallel with the patient's observation by a psychologist/psychotherapist.Acetylcysteine-based preparations are not approved in the Russian Federation as a treatment for onychophagia and cannot be unequivocally recommended to patients without their information and expert opinion of colleagues. 

Conclusion
Onychophagia is a complex interdisiplinary problem that requires a special approach to the patient. Dermatologists during routine appointments play a crucial role in the diagnosis and treatment of patients with onychophagia, which directly affects the speed of patient recovery and reduction of social maladaptation. Further development of treatment methods and options for interdisciplinary interaction between specialists of different profiles is necessary for a faster and more effective solution to the problem of onychophagia. 

 

About the authors

Tatyana Alexandrovna Gosteva

LLC "Kurchatov Center for Modern Medicine"

Author for correspondence.
Email: ya-lisenok-@mail.ru
ORCID iD: 0000-0003-0059-9159

Deputy chief physician for clinical and expert work; general practitioner, pulmonologist

therapeutic department

outpatient department

Russian Federation, 307250,Russia, Kurchatov city, Energetikov street, 10

Roman Vladimirovich Saraniuk

Dermatology and Venereology "Derma Expert"

Email: roman.saranuk@gmail.com
ORCID iD: 0000-0001-9676-1581

Dermatovenereologist

dermatovenerology department

outpatient department

Russian Federation, 305006,Russia, Kursk, Anatoly Deriglazov Avenue 1, office 3.

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