key: cord-0018744-pmo33r0s authors: Buttars, Benjamin; Braswell, Mark A.; Huynh, Thy; Badon, Hannah; Daniel, C. Ralph; Brodell, Robert T. title: Congenital malalignment of the great toenail and onychomadesis in monozygotic twins date: 2021-06-04 journal: JAAD Case Rep DOI: 10.1016/j.jdcr.2021.05.027 sha: 65c096108e6f88ba61850c3105b560b9c1059a90 doc_id: 18744 cord_uid: pmo33r0s nan Congenital malalignment of the great toenails (CMGTs) may result in onychocryptosis, a disappearing nail bed, paronychia, Beau lines, onychomadesis, retronychia, or erosion of the nail bed. 1, 2 Onychomadesis is a spontaneous arrest of the nail plate that leads to nail shedding and is a more severe manifestation of the same pathophysiologic process that produces Beau lines. 3 Onychomadesis is commonly seen as a delayed onset effect of hand, foot, and mouth disease. 4 Infectious diseases, trauma, autoimmune/systemic diseases, and medications may also injure the nail matrix, leading to onychomadesis. [5] [6] [7] [8] Rare cases of idiopathic forms of onychomadesis include familial autosomal dominant inheritance, as well as sporadic genetic mutation. 3 This case illustrates the possible link between CMGT and onychomadesis. Eleven-year-old male monozygotic twins presented with a lifelong history of abnormal growth and discoloration of the bilateral great and second toenails. The past medical history for the first twin was significant for ventriculoperitoneal shunt placement for communicating hydrocephalus at birth and surgical occlusion of a patent ductus arteriosus and unremarkable for the second twin. During infancy, both the twins had abnormal first and second toenail plates. Neither twin had any toenail pain or pain with ambulation. Fungal cultures of the great toenail clippings demonstrated no fungal growth. There was no improvement following a therapeutic trial of griseofulvin 20 mg/kg for 4 months and oral terbinafine 125 mg daily for 12 weeks. Physical examination of both twins revealed yellow discoloration, lateral deviation of the great toenail, and multiple complete transverse indentations with nail plate separations (Beau lines) involving the first and second toenail plates (Fig 1) . Several nail plate separations were full thickness, illustrating a complete spontaneous arrest of the nail matrix. Due to the onset, presentation, and chronic condition of their toenails, both patients were diagnosed with onychomadesis secondary to CMGT. The patients were instructed to wear properly fitted shoes, practice good nail hygiene, and trim nails horizontally and not round at the edges to decrease the chances of an ingrowing nail. Surgical intervention, such as complete nail matrixectomy, was not recommended for these asymptomatic twins. Most nail pathologies are slow healing and can be complicated to treat. Beau lines occur when the matrix ceases to produce nail keratin and the nail moves distally, resulting in depressions or breaks in the integrity of the nail plate. 3, 4 Complete shedding of the nail occurs when the nail plate distal to the Beau line separates from the nail bed (Fig 2) . Onychomadesis of various causes is related to the arrest of nail matrix growth (Table I ). In CMGT, lateral displacement of the nail apparatus causes recurrent, shearing microtrauma to the nail matrix that would not occur in properly aligned toenails. As such, CMGT increases the risk of various forms of nail dystrophy, including paronychia, retronychia, onycholysis, onychogryphosis, and onychocryptosis. 8, 9 We report that the identical genetically determined malalignment of the 4 toenails in the twins that was associated with weight gain and activities of daily living during pubescence, increases the strain on the nail matrix causing recurrent arrest of the matrical growth. This results in horizontal nail depressions (Beau lines) and, ultimately, onychomadesis. Efforts to prevent onychomadesis include minimization of trauma, treatment of any underlying systemic disease, and discontinuation of inciting medications such as chemotherapy. In CMGT, the shearing forces produced with normal ambulation probably cannot be prevented by measures such as avoiding ill-fitted shoes and choosing shoes with a wide toe box. Despite this, careful attention to properly sized and fitted footwear is mandatory to reduce the risk of secondary complications. Surgical options include removal and reimplantation of the nail matrix. 10 In adults with recurrent onychomadesis and onychogryphosis, complete phenol nail matrixectomy may be required. Generally, surgical options become a priority only when patients become symptomatic with recurrent infection and painful onychocryptosis. 1 This rare case shows a clear association between CMGT and onychomadesis. The extended period of the necessary treatment window and the imperfect nature of the available preventive treatment make it difficult to establish whether the patients will benefit from our suggestions. Congenital malalignment of the big toe nail An update on the disappearing nail bed Idiopathic sporadic onychomadesis: case report and literature review Onychomadesis secondary to hand-foot-mouth disease: a frequent manifestation and cause of concern for parents Onychomadesis following varicella infection: is it a mere co-incidence? Onychomadesis with lichen planus: an under-recognized manifestation Onychomadesis following cutaneous vasculitis Congenital malalignment of the great toenails: a review Beau lines, onychomadesis, and retronychia: a unifying hypothesis Etiology and treatment of nail malalignment None disclosed.