Lichen Planopilaris and Frontal Fibrosing Alopecia: They Look different 'In Person" but Practically Identical "Under the Microscope"

LPP and FFA: It’s the Clinician not the Pathologist that Tells them Apart

Classic lichen planopilaris (LPP) is a scarring alopecia that affects the central scalp. Other areas can also be affected but often the central scalp is involved. Patients with classic LPP develop scalp itching, burning and tenderness and experienced increased hair shedding as well as redness in the scalp.

Frontal fibrosing alopecia (FFA) is said to be a subtype of LPP but it has somewhat different features. It affects women to a far greater extent than men. The frontal hairline is often affected but eyebrows, eyelashes, body hair can be affected. Patients with FFA may have LPP as well.

FFA and LPP Are Distinguished by Clinical Features

FFA and LPP are distinguished in the clinic based on where the hair loss is located. FFA typical causes a more band-like area of hair loss in the frontal scalp as a main feature. Classic LPP affects various regions of the scalp but does not cause a band like area of scarring.

Several studies over the years have tried to examine whether scalp biopsies can confidently distinguish FFA and LPP. In other words, do biopsies of LPP and FFA look different or not?

Galvez-Canseco and Sperling, 2018

A study by Galvez-Canseco and Sperling in 2018 set out to examine this very question. The authors found that for all practical purposes, FFA and LPP can’t be confidently differentiated under the microscope. FFA was likely more likely to have a greater number of catagen-telogen hairs and less likely to have severe perifollicular infiltration and less likely to have a zone of concentric lamellar fibroplasia. Nevertheless, some cases of FFA were identical to LPP so these criteria alone are not sufficient to distinguish LPP and FFA under the microscope.

Poblet et al, 2006

Studies comparing LPP and FFA are not new by any means. Poblet et at in 2006 set out to compare LPP and FFA. They again found similarities. They found just a few subtle differences inlcuding fibrosis in the papillary dermis in LPP, colloid bodies in LPP, a perivascular infiltrate in LPP whereas more apoptotic cells and a milder licheoid reaction were seen FFA.

Wong and Goldberg, 2017

Wong and Goldberg added a few more observations to understanding FFA and LPP. They found that inflammation in FFA is more likely to extend below the isthmus compared to LPP. Again, it’ not a diagnostic feature by any means. 92 % of FFA biopsies had inflammation that extended below the isthmus compared to only 63 % of biopsies in LPP.

Pedrosa et al, 2017

Pedrosa et al proposed that hypertrophic sebaceous glands with and an absence of vellus hairs was a feature more likely seen in FFA than LPP.

Conclusion

FFA and LPP are distinguished in the clinic by the clinician NOT in the pathology lab by the pathologist.

REFERENCE

Galvez-Canseco A and Sperling L. Lichen planopilaris and frontal fibrosing alopecia cannot be differentiated by histopathology. J Cut Pathol 2018; 45: 313-317.

Pedrosa et al. Journal of the American Academy of Dermatology, 2017; 77:764-6.

Poblet et al. Frontal fibrosing alopecia vs lichen planopilaris: a clinicopathological study. Int J Dermatol 2006.

Wong D and Goldberg L. Journal of the American Academy of Dermatology, 2017; 76:1183-4.