Diagnostic Challenge – Lichen Striatus
A 4-year-old girl with a history of methicillin-resistant skin infection scraped her knee and developed a crusted weeping sore, to which a topical antibiotic cream was applied. One month later, a large psoriasiform plaque remained on her knee and a papulosquamous eruption extended down her leg from the popliteal fossa to the dorsal foot, following Blaschko’s lines. Topical triamcinolone cream relieved minor itching. What’s your diagnosis?
Diagnosis: Lichen Striatus
A nurse practitioner diagnosed the girl’s lesions as eczema or psoriasis. A dermatologist suggested it was lichenoid dermatitis, possibly lichen striatus.
Dr. Richard P. McClintock Jr., a dermatologist in private practice in Ukiah, California, who saw the patient upon referral, obtained the histopathology and confirmed the diagnosis of lichen striatus.
The histopathology showed lichenoid dermatitis with dyskeratotic keratinocytes scattered through the epidermis. A deep component to the lymphocytic infiltrate involved eccrine structures. Eccrine hidradenitis was present, which is a feature of lichen striatus but rarely is seen with lichen planus.
Dr. McClintock submitted the case for discussion at the annual meeting of the Pacific Dermatologic Association.
The pattern of the papulosquamous eruption in this case is “sort of a classic presentation” for lichen striatus, commented Dr. Scott Binder of the University of California, Los Angeles, and the discussant at the meeting.
Histologically, Dr. Binder focused on the spongiotic dermatitis with a lichenoid and perivascular infiltrate. He noted prominent necrosis of keratinocytes. “There’s involvement of the eccrine coils by the lymphocytic infiltrate – that’s a very important feature in discriminating this entity” from lichen planus, he said. There is often involvement of the deep vascular plexus by lymphocytic infiltrate, as in this case, he added.
Dr. Binder noted features that help distinguish lichen striatus from lichen planus. In lichen planus, generally more necrotic keratinocytes are present, “and they tend not to be at the junction like they are with lichen planus,” he said. “You don’t get a lot of really good colloid bodies in lichen striatus, although you may get a few. This particular case did not have many.”
Very often in lichen striatus but not in lichen planus, the infiltrate will go deep, in a perieccrine distribution. There’s often much more spongiosis in lichen striatus, but spongiosis tends to be trivial with lichen planus.
The presence of spongiosis opened the door to many other differential diagnoses including subacute eczema (“if you don’t look more carefully,” he said), pityriasis of the knee, and others.
“In this case, histology was very helpful,” Dr. Binder said. “So often when we’re looking at inflammatory skin disease, there’s so much histologic overlap, it can be very difficult to make a discrimination. This is a really nice case to show that histology sometimes really can make a difference, even in an inflammatory skin disease.��
Some clinicians question whether the difference between lichen striatus and lichen planus matters, he noted. “When you look at the literature, there is some suggestion that there may be an overlap between lichen planus and lichen striatus, and that these entities might be two poles of a spectrum,” he said.
Many case reports describe patients who have both lichen planus and lichen striatus, and some reports describe patients who first get one – usually lichen striatus – and then develop the other.
The patient continued the triamcinolone cream, and the eruption cleared 5 months later.
Dr. McClintock and Dr. Binder reported having no pertinent conflicts of interest.
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