What is Hori's nevus (ABNOM)?Hori's nevus (acquired bilateral nevus of Ota-like macules or ABNOM) is a hamartoma of dermal melanocytes.
ABNOM is an acquired form of dermal hyperpigmentation on the face. Hori's nevus clinically present as multiple, speckled, bilateral, blue-brown and/or slate-gray lesion occurring on the face. ABNOM are more commonly observed on the malar regions (cheek bone) and less commonly on forehead, upper eyelids, cheeks and nose. Normally in ABNOM no ocular or mucosal involvement is seen. Histopathologic studies support the view that ABNOM is a separate entity from Ota lesions.
ABNOM causesThe pathogenesis of ABNOM is not known. One theory proposes the cause of Hori's nevus as dropping-off of epidermal melanocytes in the basal layer of epidermis into dermal layers. Another view proposes activation of preexisting latent dermal melanocytes by some triggering factor into ABNOM. Some researchers attribute an association with female hormones as the prevalence of Hori's macules is higher in women during their reproductive age. In another study by Long et al., it was found that the expression of androgen receptors increase in ABNOM lesions, whereas estrogen and progesterone receptors expression do not increase.
ABNOM diagnosisHori's macules are not present at birth. ABNOM may initially present be as discrete brown patches. Hori'S nevus may progress with time to acquire slate-grey color. Hori's macules have irregularly shaped bipolar melanocytes with many singly dispersed melanosomes. In Hori's nevus, the melanocytes are dispersed in the middle and the upper dermis and the skin structure is not disturbed. Melanocytes in ABNOM are dispersed in the perivascular areas of dermis.
ABNOM abnormal manifestationsHori's macules in some rare cases may involve mucous membranes. Ramesh M Bhat et al reported a case of ABNOM with a mucosal involvement in a 42 year old South Indian male patient. He had "multiple, discrete, speckled, blue-gray to slate-gray, hyperpigmented macules, symmetrically distributed on either side of the face, involving the forehead, anterior aspect of the scalp, bilateral temporal, zygomatic, malar areas, upper eyelids, nose, and pinnae. Blue-brown discoloration of both sclera and a hyperpigmented irregular mottled patch over the hard palate was also noted." Based on clinical and histopathological findings it was diagnosed as Hori's macules.
In some rare cases both Ota and Hori's macules can be present in the same patient. Jung-Hun Park et al reported a case of simultaneous presence of Ota macules and ABNOM in a 36-yr-old Korean woman. She had dark bluish lesion on her right cheek and right conjunctiva since birth. She also had mottled brownish macules on both sides of forehead and both sides of lower eyelids that have developed three years ago. With histopathological studies the team diagnosed the lesion on the right cheek as nevus of Ota and and those macules on the forehead and eyelids as ABNOM.
ABNOM treatmentABNOM has been successfully treated with pigment-specific lasers including the Q-switched Nd: Yag laser (1064 nm), Q-switched alexandrite laser (755 nm), and Q-switched ruby laser (694 nm). The concurrent use of QS 532nm Nd:YAG in combination with the QS 1064nm Nd:YAG laser had also given successful results in treating Hori's nevus.
Reference: 1.Park JH, Lee MH. Acquired, bilateral nevus of Ota-like macules (ABNOM) associated with Ota's nevus: case report. J Korean Med Sci. 2004 Aug;19(4):616-8.
2.Park JM, Tsao H, Tsao S. Acquired bilateral nevus of Ota-like macules (Hori nevus): etiologic and therapeutic considerations. J Am Acad Dermatol. 2009 Jul;61(1):88-93.
3.Bei-Qing Wang, Zheng-Yu Shen, Ye Fei, Hong Li, Jian-Hang Liu, Hui Xu, Zhen Zhang, Xiao-Hong Yu, Xiang-Dong Chen. A Population-Based Study of Acquired Bilateral Nevus-of-Ota-Like Macules (ABNOM) in Shanghai, China. Journal of Investigative Dermatology (2011) 131, 358–362.
4.Polnikorn, N., Tanrattanakorn, S., Goldberg, D. J. (2000). Treatment of Hori's Nevus with the Q-Switched Nd:YAG Laser. Dermatologic Surgery, 26: 477–480.
5.Bhat RM, Pinto HP, Dandekeri S, Ambil SM. Acquired bilateral nevus of ota-like macules (ABNOM) with Mucosal involvement: A new variant of Hori's nevus. Indian J Dermatol 2014;59:293-6