Towards better clinicopathologic diagnosis of lichen planus

Vulvovaginal lichen planus (LP) is a T-cell mediated inflammatory dermatosis characterised by quality of life impacts, irreversible anatomic changes, long-term treatment, and a reported increase in vulval cancer risk. Major knowledge gaps include that there are no consensus-based diagnostic criteria, no validated outcome measures, and little agreement on treatment strategies. The lack of diagnostic criteria produces a major limitation of clinical studies - not all participants have the disease of interest. Progress on diagnostic criteria is hindered by a lack of histopathologic research. The thesis aim was to address deficiencies in the clinicopathologic literature on vulvovaginal LP in order to lay the groundwork for international consensus guidelines on diagnosis. Methodology for all studies was similar. The local pathology database was searched for diagnoses of interest. Slides were reviewed to select specimens meeting inclusion and exclusion criteria, then assessed for histopathologic features. Clinical notes and photographs were obtained from referring specialists. Clinical and histopathologic data were analysed together in an effort to describe patterns of presentation and diagnostic conundrums. There are six key findings of the nine incorporated studies. • Determination of anatomic site is fundamental to establishing a diagnosis. • LP often presents with infectious and dermatologic comorbidities; identification requires liberal use of microbiology and biopsy at morphologically-distinct areas. • There are two patterns of basal layer abnormality in erosive LP: the well-known degenerative pattern, and the newly described regenerative pattern. • Non-recognition of the regenerative pattern contributes to the high non-diagnostic biopsy rate, along with clinician factors such as suboptimal biopsy timing or placement, and mistaking candidosis or vulvodynia for LP. • Classic and hypertrophic LP have complex clinicopathologic appearances with multiple avenues for misdiagnosis. • The evaluation of dermatosis-associated neoplasia requires an appreciation of all of the above components in order to avoid misattribution of vulvar cancers to LP.