Woolly hair nevus - Hair and Scalp
Type 1 woolly hair nevus is an isolated finding. Type 2 woolly hair nevus, which is seen in 50% of cases, is a mosaic RASopathy associated with linear verrucous epidermal nevus. Type 3 wooly hair nevus is acquired in young adults and is also known as acquired progressive kinking of scalp hair.
Woolly hair nevi can also be associated with ocular findings including heterochromia iridis and persistent pupillary membrane. Auditory, dental (diastema, decayed lower canine teeth), skeletal (growth impairment, brachyphalangy), and renal anomalies have also been identified.
A few cases of woolly hair nevus in patients with incontinentia pigmenti have been reported.
Q84.1 – Congenital morphological disturbances of hair, not elsewhere classified
239124001 – Woolly hair nevus
Differential Diagnosis & Pitfalls
- Hereditary woolly hair – Autosomal dominantly inherited. The entire scalp has woolly hair. If the patient has a large woolly hair nevus, this can be difficult to distinguish. Look for nevus to have circumscription and lack of family history.
- Autosomal recessive woolly hair / hypotrichosis (ARWH/H) – Caused by mutations in the lipase H (LIPH) or keratin 25 (KRT25) genes.
- Naxos syndrome
- Carvajal syndrome
- Uncombable hair syndrome – Silvery hair with texture of "spun glass." This will be a diffuse condition involving the entire scalp. A positive family history may be uncovered.
- Pili torti – Can have focal areas of shortened, brittle hair with characteristic trichogram features; flattened and twisted hair.
- Trichorrhexis nodosa (TN) – Because the hair may be more fragile, concomitant TN is common, but close evaluation demonstrating the tight coiling should make it clear that the TN is a secondary phenomenon.