N-Acetylcysteine in Trichotillomania: Comparison
Please note this is a comparison between Version 2 by Camila Xu and Version 1 by Debra Lee.

N-acetylcysteine (NAC) (C5H9NO3S) is the acetylated precursor of the amino acid L-cysteine and functions as a glutamate modulator and antioxidant. It is widely known as a mucolytic, an antidote for acetaminophen overdose, and a nephroprotective agent for contrast administration. Trichotillomania (TTM), excoriation disorder, onychophagia, and onychotillomania are categorized as body focused repetitive behavior (BFRB) disorders, causing damage to the skin, hair, and/or nails with clinically significant psychosocial consequences.

  • N-acetylcysteine
  • NAC
  • body focused repetitive behavior
  • BFRB

1. Introduction

Body-focused repetitive behavior (BFRB) disorders are self-inflicted, compulsive behaviors that cause physical damage to the skin, hair, and nails, often with psychosocial consequences. There is increased research interest in BFRBs, encompassing both psychiatry and dermatology disciplines. Approximately 30% to 40% of patients treated for dermatological conditions suffer from an underlying psychiatric disorder that worsens or causes the skin disease [1]. Common BFRBs include trichotillomania (TTM) (hair pulling), excoriation disorder (skin picking), onychophagia (nail biting), and onychotillomania (nail picking). Mild forms of these behaviors are relatively common in the general population; however, severe cases can cause significant distress or impede social functioning.
All BFRBs are now classified under obsessive compulsive and related disorders (OCRD) in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) [2]. The DSM-5 makes a distinction between BFRBs and OCRDs, stating that BFRBs are not triggered by obsessions or preoccupations, but may be preceded or accompanied by feelings of anxiety or boredom [2]. In addition, OCRD behaviors do not arise from a fixation on the body, but are provoked by other factors [2,3][2][3]. It is estimated that 1 in 20 people suffer from a BFRB [4]. The prevalence ranges from 0.5–2% for TTM [1[1][2][5],2,5], 1.4–5.4% for excoriation disorder [2[2][6],6], 20–30% for onychophagia [7], and 0.9% for onychotillomania [7].
Although the pathophysiology of BFRBs is incompletely understood, neuroimaging studies in patients with OCD and OCRDs have consistently shown hyperactivity in the orbitofrontal cortex and striatum [8,9][8][9]. It is hypothesized that this hyperactivity is due to an increased excitation to inhibition ratio from increased glutaminergic excitation or reduced GABAergic inhibition, resulting in the compulsive behaviors seen in BFRBs [10,11][10][11].
Effective pharmacologic treatments for BFRBs are lacking. Currently, there are no Food and Drug Administration-approved drugs for BFRBs, and psychotropic drugs with numerous side effects are often used as first-line therapy with mixed results. However, there is a growing body of evidence for the use of glutaminergic agents for treating BFRBs and OCRDs, namely N-acetylcysteine (NAC).
NAC (C5H9NO3S) is the acetylated precursor of the amino acid L-cysteine and functions as a glutamate modulator and antioxidant [12,13,14,15,16][12][13][14][15][16]. It is widely known as a mucolytic, an antidote for acetaminophen overdose, and a nephroprotective agent for contrast administration [15,17][15][17]. NAC attenuates glutaminergic hyperactivity by releasing glutamate, the main excitatory neurotransmitter in the central nervous system, into the extracellular space. This stimulates inhibitory glutamate receptors and reduces glutaminergic neurotransmission [1,16][1][16]. Excessive amounts of glutamate discharge results in neuronal damage and is associated with many repetitive and compulsive disorders. Significantly higher levels of glutamate have been found in the cerebral spinal fluid, orbitofrontal cortex, and caudate nucleus of OCD patients [18,19,20][18][19][20]. Through this mechanism of action, NAC has been successfully used as adjunctive treatment in many psychiatric mood disorders (i.e., depression, anxiety, and post-traumatic stress disorder (PTSD)) [12,21][12][21].
Abnormalities in the dopamine pathway are associated with psychiatric disorders including schizophrenia, addiction, depression, and attention deficit hyperactive disorder (ADHD). NAC indirectly regulates dopamine release through glutaminergic neurotransmission, acting on the presynaptic mGlu2/3 receptors [22]. Additionally, dopamine, glutamate, and their oxidized metabolites can be cytotoxic and contribute to oxidative stress [23,24,25][23][24][25]. NAC protects cells against oxidative stress by replenishing glutathione, a major antioxidant made up of glutamate, glycine, and cysteine. NAC contributes cysteine, the rate-limiting substrate of glutathione synthesis [15]. Cysteine is also an effective free radical scavenger, further minimizing inflammatory and oxidative stressors. Reduction of cellular oxidative stress is thought to block the reinstitution of compulsive behaviors [3,17][3][17].
Compared to other glutaminergic agents, NAC has received much attention for its use in treating BFRBs given its low cost and benign side effect profile. More recently, there is increasing evidence on the efficacy of NAC in treating BFRBs.

2. NAC in Trichotillomania

TTM is repetitive hair pulling of one’s own hair from the scalp, eyebrows, eyelashes, and pubic region, leading to nonscarring patchy hair loss with short hair. Patients have a negative hair pull test on physical examination. This condition is exacerbated by stress and can cause significant distress, shame, and low self-esteem. First-line pharmacologic treatments for TTM are selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs), specifically clomipramine [1]. Other drugs studied for treating TTM include olanzapine, inositol, and naltrexone with limited success [1,27,28,29][1][26][27][28]. NAC has been studied in several clinical trials for TTM treatment (Table 1) [30,31,32,33,34,35,36,37,38,39,40,41][29][30][31][32][33][34][35][36][37][38][39][40].
Table 1. Summarizes all NAC treatment studies for TTM, which includes one adult and one pediatric randomized double-blind controlled trials and nine case reports.

References

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