As previously mentioned, there is overlap amongst the differential diag- noses mentioned for generalized vitiligo and segmental vitiligo. As such, in addition to the following disorders, any of the previously mentioned disorders can present with hypopigmenting lesions in a segmental or focal distribution.
Naevus depigmentosus
Naevus depigmentosus can either be a congenital hypopigmenting disor- der or, less commonly, form during adolescence or adult life. The macules or patches may not be noticed until later in infancy. Relatively stable in size throughout its life, it is well circumscribed, irregular bordered,
hypopigmented, solitary and often unilateral. Its size will vary depending on if it is isolated, segmental or systematized. Hairs within the naevus may be hypopigmented. The lesions are commonly located on the trunk or prox- imal extremities (Figs 14.20 & 14.211, however, may occur on the head and neck. Histological and electron microscopic studies reveal normal or decreased numbers of melanocytes and few melanosomes, as well as abnor- mal melanization within the melanocytes (Pinto & Bolognia 1991). Differen- tiation from segmental vitiligo is based on the age of onset and hypopigmentation vs. depigmentation.
Naevus anaemicus
Naevus anaemicus can also be a congenital or acquired anomaly of hypochromic macules and patches. However, there is no true abnormality in the pigmentary system. The lesion is caused by decreased blood flow through the capillaries in the dermal papillae. A hypochromic or pale lesion of variable size with well defined borders and irregular margins will present at birth but is often missed until later on in life (Fig. 14.22). Usually unilateral and located on the trunk, it is not accentuated by Woods lamp examination. Pressure at the margin of the lesion obliterates the border making the lesional skin indistinguishable from surrounding skin. This is best demonstrated on diascopy. Histological and electron microscopic
Fig. 14.20 Naevus depig- mentosus.
CHAPTER 14
Differen f ial Diagnosis
Fig. 14.21 Naevus depig- mentosus.
117
CHAPTER 14
Differential Diagnosis
studies reveal no abnormality in melanocytes or melanization. Naevus anaemicus is felt to be due to a localized hypersensitivity of blood vessels within the lesion to catecholamines (Mountcastle et al. 1986). Naevus anaemicus is easily distinguished from segmental vitiligo based on clinical and histological findings.
Topical steroids
Although unlikely to be confused with vitiligo, hypopigmentation after intralesional corticosteroid therapy can occur in a focal distribution. The lesion is characterized by linear, irregular and stellate or angulated, ill- defined, hypopigmented streaks often occurring several weeks to months after intralesional or intra-articular injections of steroids (Figs 14.23 &
14.24). The pattern of hypopigmentation is felt to be secondary to lym- phogenous spread of the corticosteroid suspension. Histological and elec- tron microscopic findings in one patient revealed decreased numbers of melanocytes in the hypopigmented skin (Friedman et al. 1988). Repigmen- tation is variable. A history of intralesional or intra-articular injection should be obtained. If not, the pattern and ill-defined border of the lesion rule out vitiligo.
Fig. 14.22 Naevus anaemicus.
Fig. 14.23 Leukoderma secondary to intra-articular Kenalog.
CHAPTER 1 4
Different id Diagnosis
Fig. 14.24 Steroid-induced hypopigmentation.
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