BHD and Tuberous sclerosis (TSC) – Part II: Skin Lesions

The skin lesions that develop in BHD Syndrome and TSC are remarkably similar and appear to be confined to the facial/neck region of patients: fibrofolliculomas and trichodiscomas occur in BHD patients and originate from hair follicles, whilst angiofibromas (characteristic of TSC) also develop from hair follicles but also consist of connective tissue and blood vessel components.  So histologically, they are very similar but still remain clinically distinct entities.

Luckily, Misago et al (2009) carried out a study investigating the similarities between the skin lesions found on individuals with BHD and TSC. Now, if you’re au fait with dermatology go, check out the link but for those of you who don’t know your ‘sebacious lobules’ from your ‘perifollicular whorls’ here’s the take home message of the study:

  • Confirmation of similarities between histopathological components between angiofibromas and fibrofolliculomas.
  • The expression profiles of specific proteins were similar between the two lesions suggesting similar mechanisms of development. These include:
    1. CD34 and Factor XIIIa: adhesion molecules within the extracellular matrix;
    2. Nestin: a biomarker for angiogenesis;
    3. C-kit: a tyrosine receptor thought to play an important role in hematopoietic stem cell development. Its expression in this context remains unclear but is thought to participate in the development and maintenance of hair follicles.
    4. Preserved CK15 expression: this protein is usually seen in undifferentiated tissues and its presence here seems abnormal.

These findings indicate that these clinically distinct lesions from two different syndromes have a common histogenesis such as abnormal function of hair follicles and surrounding tissue. This may indicate a common (or at least related) biological cause too and I feel merits further investigation.

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