A KOH (potassium hydroxide) test done at the visit was negative as well as a fungal culture of each toenail.
The patient was diagnosed with congenital malalignment of the great toenails (CMGTN) based on history and morphologic appearance.
Congenital malalignment of the great toenails is an underrecognized and underreported nail disorder characterized by lateral deviation of the nail plate, which is not parallel to the longitudinal axis of the distal phalanx.1 The cause is unknown. Some reports suggest a genetic cause being transmitted in an autosomal dominant fashion with variable expression.2 There have been reports of CMGTN in monozygotic and dizygotic twins making this theory likely.3 Other authors consider an external cause such as amniotic bands, neonatal asphyxia, vascular malformations, and uterine pressure. This condition also has been reported in patients with Rubinstein-Taybi.4
The nail changes can occur at birth but in some cases, such as our patient, the nails become dystrophic months to years after birth. Characteristic nail changes include shorter, discolored, hyperkeratotic nails with transverse groove or ridges. In some cases, the dystrophic nails may cause inflammation and tenderness and is the most common cause of ingrown toenails in children.
The differential diagnosis includes onychomycosis, traumatic nails, nail psoriasis, pachyonychia congenital (PC), and onychomadesis. Onychomycosis can present with white or yellow discoloration of the nail that in some cases can be associated with nail breakage, hyperkeratosis, onycholysis, and subungual debris. Either fungal culture or periodic acid shift stain of nail clippings can help confirm or exclude this diagnosis. Psoriatic nails present with nail pits, oils spots, and onycholysis. Traumatic nail changes may occur from using small shoes and trauma from running or playing soccer, and presents with subungual hemorrhage and nail dystrophy of the first or second toenail. PC is a genetic disorder caused by a mutation in certain keratin proteins of the skin (k6a, k6b, K16 and K17). These patients usually have other skin findings including palmoplantar keratoderma, white plaques on the mouth, and skin cysts (steatocystoma multiplex and vellus hair cysts). Nail changes characteristic of PC includes subungual hyperkeratosis that causes a wedge shape thickening of the nail bed (pincer nails).5 Onychomadesis can be seen after viral infections such as hand-foot-mouth disease or in patients taking chemotherapy drugs that affect nail growth.
CMGTN usually resolves with time, but some patients with severe deviation and paronychia may need surgical correction.6
Dr. Matiz is a pediatric dermatologist at Southern California Permanente Medical Group, San Diego. Email her at firstname.lastname@example.org.