Pili annulati (PA), or ringed hair is a hair condition where alternating segments of light and dark hair are visible on individual strands when they are exposed to bright or reflective light. Hair appears to be covered with shiny dots or stripes of color. The permanent non-progressive condition may occur alone, with alopecia areata, or be a symptom of a disease called autosomal recessive hypohidrotic ectodermal dysplasia. Pili annulati usually develops by the age of two.
The exact cause of pili annulati is not known, but it is passed on though an autosomal dominant gene. Ringed hair may be caused by a metabolic protein deficiency that leads to the abnormal formation of cytoplasmic ribosomes with the hair’s cells, resulting in the unusual formation of keratin within the cortex of the hair. Most cases are believed to be caused by a mutation in the keratin forming cells of the hair follicle.
Diagnosis of pili annulati may occur after a visual examination of the hair strands by a physician. A microscopic examination of the hair shaft may be needed to confirm the diagnosis. Under a microscope in reflected light, irregular spaces are observed in between areas of normal hair growth. Empty spaces within the strand of hair reflect light, giving the impression of rings or dots within the strand. The hair strands are usually lacking the full amount of keratin that is normally found in most hair.
Symptoms of pili annulati are varied. In addition to the different colored bands on each strand of hair, the hair may be abnormal brittle. Hair loss often occurs due to the rapid breakage of the hair strands. An adult with PA may notice that armpit hair and other body hair has the same ringed appearance.
Pili annulati does not usually require any treatment. Medicated shampoos that encourage the re-growth of hair may be recommended to treat possible hair loss. Gentle brushing may help brittle strands of hair remain whole. Since ringed hair may be caused by or be part of another medical condition, a physician may recommend further testing if hair strands show signs of pili annulati.
Autosomal recessive hypohidrotic ectodermal dysplasia is characterized by malformations of the hair, teeth, and skin. A person with this condition may also have missing teeth and very thin hair. Small hard bumps called follicular hyperkeratosis often develop on the body, arms, and legs. A skin biopsy will show that the sweat glands have not developed.