Some people with alopecia areata develop changes to their nails

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Alopecia Areata 
Alopecia Areata Biology
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  The Nails in Alopecia Areata
 
One of the clinical features of alopecia areata is aberrant nail formation. This feature is found in almost 10% to 66% of people affected by this disease. These nail changes usually occur along with hair loss but may occur earlier or later than the hair shedding, by months or years. Examination of these nail changes gives a good idea about the severity of the disease. For instance, marked nail dystrophy is an indicator of either total scalp hair loss called alopecia totalis, or loss of all body hair, called alopecia universalis.

Nail plates or fingernails are keratin products produced by a kind of modified epidermis. This modified epidermis, called the nail matrix, is the root of the nail. Keratin is a protein complex and it is this keratin which makes the nail hard and thus well suited for its primary function that is protection.

Nail anatomy reveals three separate parts. The upper third of the nail plate develops from the proximal part of the matrix. The lower two thirds of the nail plate develop from the distal part of the matrix. The third part, the subungual keratin, corresponds to the horny layer of the root of the nail. It is also called the nail bed. As the nail grows, the distal part provides the deeper layers of the nail plate and the proximal part provides the superficial layers. The crescent shaped whitish mark, sometimes seen at the base of the nail is actually under the nail plate. This mark indicates the presence of keratin cells, which have not been flattened and still retain their content.

Clinical Features of Nail Changes

It is the structure of the normal nail that decides the clinical features of the affected nail. The clinical features depend on the localization or severity of the disease. If the proximal part of the matrix is affected, then onychorrhexis or brittle nails and irregular pits are seen. If both the distal and proximal parts are affected then a thinned out nail plate is observed. This thinning may be linked to a compensatory hypertrophy of the root of the nail and may lead to complete destruction of the plate and the nail may eventually be shed.

Nail aberrations, which are clinically attributable to alopecia areata are therefore very varied though they are all expressions of a matrix disease. These nail abnormalities can affect one, some or all nails

Despite considerable work, the causes of such aberrations are by and large still unknown. Some of the common nail aberrations are the following:

  • Nail pitting: This is the most common nail aberration. The disease causes irregular keratinization on the nails. These irregular keratins fall off from the nails leaving behind depressions or pits.
  • Onychorrhexis: These are brittle nails having vertical ridges, which sometimes split vertically and peel off.
  • Onychomadesis occurs when the proximal part of the nail separates from the nail bed, leading usually to shedding. The nail may or may not grow back.
  • Onycholysis is the separation of the distal part from the nail bed.
  • Koilonchia: Here the outer surface of the nail acquires both longitudinal and transverse concavity giving it a spoon-like appearance. It is due to thinning out of the nail plate.
  • Spotting of the lunula is the crescent shaped mark at the base of the nail.

It must be noted that anonychia and scarring have not been observed.

Histology of Nail changes in Alopecia Areata

Nail fragments examined by light and electron microscopy show that nail aberrations are linked to the proximal part. While aberrations are all over the nail plate, maximum aberrations are in the upper proximal while the lower subuangal and the nail bed is almost entirely preserved. The distal part is negligibly affected.

Under light microscopy the nail plate is often seen thinned out but total atrophy is rare. There are wave like bands showing architectural disorder of the corneocyte arrangement. Also observed is parakeratososis of variable intensity. That is, the nuclei are either grouped in centers or distributed evenly throughout the plate. It is noticed that changes are more in the upper part and less in the lower part.

Particularly the upper edge shows disintegration and pits. These pits often look like thin parallel slits giving it a flaky appearance. By and large the subuangal layer is not affected and shows only light parakeratososis

Under electron microscopy the shape of the nail plate looks very clearly changed. The cytoplasm is filled with vacuoles of sizes ranging from 140 mm to 1600 mm. The keratin fibre network also looks changed. Some cells distinctly show fiber rarefaction making them look fibrillary. Lastly, the cytoplasm is sometimes seen to contain nuclei and fragments of internalized membranes. The space between cells is increased from 25-35 mm to 100-850 mm. It is still bigger in some places taking on the appearance of an ampular dilation

As under light microscopy, here also, changes are seen concentrated more in the upper part than in the lower part, with the subuangal layer remaining largely unaffected, sometimes hypertrophic.

Both, light and electron microscopy show that the disease affects the upper or the proximal part of the nail plate in a major way, the lower or distal part in a minor way while the subuangal or the nail bed is largely spared. This sort of preferential localization points to a deep disorder of the matrix keratinization.

Light and electron microscopy also show that nail aberrations can take many forms like parakeratososis, parallel slits and arachitectural disorder. These aberrations are seen even in normal nails. In the case of alopecia areata these clinical features are exacerbated. Sometimes in the normal nails cupuliform dips, corresponding to pits, are seen in the upper part of the nail plate. Therefore histology of alopecia areata does not seem to be very specific and, as such, diagnostic conclusions are difficult to arrive at. However, accompanying histological aspects like changes in the upper part of the nail plate, largely spared nail bed, parakeratososis, parallel slits and pits or dips do argue for diagnosis as alopecia areata.



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