I always enjoy rendering the diagnosis of lichen striatus – parents are concerned, the rash is benign, and usually resolves within months. The only downer is trying to answer the inevitable question of “Why did my child get this?” and I morph from the sagacious physician to a dunce, shrugging my shoulders, responding “beats me”!
Blaschko lines correlate with mosaicism, regardless of the clinical presentation. Congenital lesions may include incontinentia pigmenti and variants of epidermal nevi. Acquired Blaschkoid lesions include rare reports of psoriasis, atopic dermatitis, lupus erythematosus, fixed drug eruption, graft-versus-host disease, and erythema multiforme. The “big three” are lichen striatus (LS), adult Blaschkitis (AB), and linear lichen planus (LLP) (1).
The following are classical presentations:
LS usually occurs in childhood and is characterized by a linear array of (usually) asymptomatic violaceous to hypopigmented papules, in a discontinuous band on an extremity, occasionally associated with nail changes (striations, thinning, or onychoschizia). Most cases resolve in a year, although hypopigmentation may persist. AB is seen adults, appearing as a pruritic papulovesicles on the trunk, that appears and resolves quickly, but is often recurrent. LLP usually is seen in adulthood, manifesting as pruritic violaceous papules on the extremities; it may be rather persistent and postinflammatory hyperpigmentation is noted following resolution of the eruption. Histologically, the classical appearance of LS is a lichenoid infiltrate with deeper perieccrine involvement, AB appears spongiotic, and linear LP displays a lichenoid pattern.
Any type of clinical or histologic overlap you can imagine has been reported – LS in adulthood, interface dermatitis in AB (2), or pediatric cases of Blaschkitis (3), etc. Are these entities part of a spectrum or are they distinct?
Pathophysiologically, precipitating factors may include environmental agents, viral infection, hypersensitivity, skin injury, and a genetic predisposition in the mosaic region. Both LS and linear LP demonstrate an increase in CD1a+, CD3+, CD4+, CD8+, and CD68+ cells. Minor differences between the conditions have been noted; for example, Ki-67 and involucrin in linear LP seem to be more abundant than in LS, but it is unclear how this affects pathogenesis. Clearly, more basic studies are needed to decipher the immunologic events (4).
It is also essential that in the case of LS, the perieccrine infiltrate not be mistaken for syringotropic mycosis fungoides – in LS the infiltrate is composed of CD4 and CD8 positive cells with negative T-cell gene rearrangement studies, as opposed to cutaneous T cell lymphoma (5).
Given the potential overlapping features of LS, AB, and LLP, the unifying theory of a spectrum of disease has been advocated since the acronym BLAISE was proposed by Taieb et al (6). While I appreciate the concept, until such time that we truly understand the pathomechanisms of the disorders, I will continue to use the classical nomenclature. I find it easier to educate patients on what to expect when these diseases can be classified by their predominant features, with the understanding that there may be some degree of clinical or histopathologic similarities.
I also admit to acronym fatigue. I find it harder to remember what each letter means than knowing the features of each component illness. Perhaps it will become in vogue to cut back on new acronyms. LOL.
- Johnson M, et al. Interface dermatitis along Blaschko’s lines. J Cutan Pathol 2014; 41: 950-4.
- Suárez-Peñaranda JM, et al. Unusual interface dermatoses distributed along Blaschko’s lines in adult patients. Am J Dermatopathol 2017; 39: 144-9.
- Keegan BR, et al. “Pediatric blaschkitis: Expanding the spectrum of childhood acquired Blaschko-linear dermatoses. Pediatr Dermatol 2007; 24: 621-7.
- Zhou Y, et al. Lichen striatus versus linear lichen planus: a comparison of clinicopathologic features, immunoprofile of infiltrated cells, and epidermal proliferation and differentiation. Int J Dermatol 2016; 55: e204-10.
- Wang L, et al. Lichen striatus with syringotropism and hyperplasia of eccrine gland cells: A rare phenomenon that should not be confused with syringotropic mycosis fungoides. J Cutan Pathol 2016; 43: 927-31.
- Taieb A, et al. Lichen striatus: A Blaschko linear acquired inflammatory skin eruption. J Am Acad Dermatol 1991; 25: 637-42.
*Image of Dr. Alfred Blaschko (1858-1922) from Plastic Surgery Key