While there is not a calculated incidence or prevalence for linear and whorled nevoid hypermelanosis (there is no official method for tracking rare conditions), the condition appears to be very rare given the few case reports that have been described in the medical literature. The condition usually happens as a chance occurence in a family. In total, around 45 cases have been described in the medical literature worldwide. The rare occurance of linear and whorled nevoid hypermelanosis is one reason why data and information regarding the condition is lacking. Rare conditions can present an especially challenging situation. Since some conditions are so rare, there are few cases to learn from, let alone conduct research.
Last updated: 3/18/2013
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Metta AK, Ramachandra S, Sadath N, Manupati S. Linear and whorled nevoid hypermelanosis in three successive generations. Indian J Dermatol Venereol Leprol. 2011 May-Jun;77(3):403; http://www.ncbi.nlm.nih.gov/pubmed/21508598. Accessed 3/18/2013.