A 24-year -old male presents with a hyperpigmented patch over the right upper chest 4 years ago, thick hair over the same with time. Diagnosis is:
Ref. Rook's Textbook of Dermatology, Pg 75
 
Becker Nevus

Sharply demarcated pigmented macule, often with localized hypertrichosis
Dermoscopy: network, focal hypopigmentation, skin furrow hypopigmentation, hair follicles, perifollicular hypopigmentation and vessels
Sex ratio close to 1:1 
Sharply demarcated, unilateral, hyperpigmented tan macule on back, shoulder or chest
Hypertrichosis in 50%

 
Histopathology

Increased basal layer pigmentation, mild acanthosis, hyperkeratosis and regular elongation of rete ridges
Variable hypertrichosis
Areas associated with smooth muscle hamartoma have more pronounced smooth muscle bundles irregularly dispersed within the dermis and unrelated to either hair follicles or vascular channels
Does not actually contain nevus cells
Spitz nevus
Hypermelanosis of Ito
Becker’s nevus
Congenital melanocytic nevus