Presentation
Primary symptoms:

sounds or speech becoming dull, muffled or attenuated
need for increased volume on television, radio, music and other audio sources
difficulty using the telephone
loss of directionality of sound
difficulty understanding speech, especially women and children
difficulty in speech discrimination against background noise (cocktail party effect)Secondary symptoms:

hyperacusis, heightened sensitivity to certain volumes and frequencies of sound, resulting from "recruitment"
tinnitus, ringing, buzzing, hissing or other sounds in the ear when no external sound is presentUsually occurs after age 50, but deterioration in hearing has been found to start very early, from about the age of 18 years. The ISO standard 7029 shows expected threshold changes due purely to age for carefully screened populations (i.e. excluding those with ear disease, noise exposure etc. ), based on a meta-analysis of published data. Age affects high frequencies more than low, and men more than women. One early consequence is that even young adults may lose the ability to hear very high frequency tones above 15 or 16 kHz. Despite this, age-related hearing loss may only become noticeable later in life. The effects of age can be exacerbated by exposure to environmental noise, whether at work or in leisure time (shooting, music, etc.). This is noise-induced hearing loss (NIHL) and is distinct from presbycusis. A second exacerbating factor is exposure to ototoxic drugs and chemicals. Over time, the detection of high-pitched sounds becomes more difficult, and speech perception is affected, particularly of sibilants and fricatives. Patients typically express a decreased ability to understand speech.
Incomplete conversion of the sulfhydryl –SH group onto S-S disulfide bonds in the protein of the cortical fibers leads to cortical softness and subsequent invagination of the fully keratinized distal hair shaft into the softer, abnormally keratinized proximal hair shaft. Intussusception of the distal hair shaft into the proximal hair shaft results in a distinctive ball-and-socket hair shaft deformity. The affected hairs are brittle and breakage is common, resulting in short hairs.Migratory lesions of ichthyosis linearis circumflexa may be caused by a dermal influx of inflammatory cells that undergo phagocytosis and digestion by keratinocytes, resulting in disruption of keratinization.Increased transepidermal water loss resulting from the disturbance of corneocyte barrier function in erythroderma may cause profound metabolic abnormalities and hypernatremia, particularly in neonates. Epidemiology
Approximately 200 cases of trichorrhexis invaginata (bamboo hair) have been reported in the literature, but the true incidence is not known. The incidence of trichorrhexis invaginata (bamboo hair) may be as high as 1 case in 50,000 population. Girls are affected more often by trichorrhexis invaginata (bamboo hair) than boys, but is present in all races. History
In 1937, Touraine and Solente first noted the association between hair-shaft defects (bamboo node) and ichthyosiform erythroderma. Còme first coined the term ichthyosis linearis circumflexa in 1949, although Rille had previously recorded the distinctive features of ichthyosis linearis circumflexa by 1922. In 1958, Netherton described a young girl with generalized scaly dermatitis and fragile nodular hair-shaft deformities, which he termed trichorrhexis nodosa.