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`Curro Probl. Derm., vol. 9, pp. 102-149 (Karger, Basel 1981)
`
`The Human Nail
`Structure, Growth and Pathological Changes
`
`U. Runne and C.E. Orfanos l
`Department of Dermatology, University of Cologne, Cologne, FRG
`
`Introduction
`
`The nail protects the delicate terminal phalanges of the fingers and toes. It
`forms a buttress for the digital pulp and aids in picking up small objects. Patho(cid:173)
`logical changes
`in the nail wall and plate make many everyday activities more
`difficult. Moreover, changes in the nails have an important cosmetic aspect, so
`that the hands of these patients are often literally tied. It is interesting from a
`clinical point of view that nail changes are often signs of dermatological or
`systemic disease and may even be their leading sign. A correct classification and
`interpretation of pathological nail symptoms is only possible if the structure,
`growth and pathology of the nail are fully understood.
`
`1. Structure of the Nail
`
`is the translucent nail plate, which is
`The essential element of the nail
`closely connected to the reddish shimmering nail bed. Proximally and laterally
`it is surrounded by the epidermal nail wall and enclosed by the groove-shaped
`nail fold. Like the matrix, the nail root, invisible and 3-5 mm deep, lies in the
`nail fold. Only the distal end of the matrix appears as the lunula; its epithelium,
`being rich in nuclei, gives the lunula its whitish color, and makes it stand out
`from the nail bed (fig. 1,2).
`Seen longitudinally, the epidermis of the proximal nail wall bends around
`the nail root and lies dorsally to it as eponychium. Its stratum corneum forms
`the cuticle. The cuticle adheres to the nail plate and protects the nail fold and
`should therefore not be removed (fig. 3). Immediately below the cuticle and
`
`1 We should lIke to thank Mrs. E. Bodeux, MISS R. Kunigk and Mrs. G. Scheffer for
`theIr hclp in preparIng thc figures and the photographs. We thank Dr. Nicholas M. Walker
`for checkIng the tramlatlOn.
`
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`
`The Human Nail
`
`_Yellow line
`
`all plate
`
`ail wall
`
`6//h'//II.. - - Lunula
`Lunula
`
`103
`
`Hyponyc lurn
`('sole hOrn' )
`
`MatrIx
`
`2
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`Localisation
`Localisation
`
`Localisation
`
`Fig.
`
`Fig.
`
`3
`
`a
`Fig.
`
`Fig. 1. (,\inically visible parts of the nail.
`Fig. 2. Localisation of matrix and 'sole horn',
`Fig. 3. Composition of the nail in longitudinal section. a = Matrix (dorsal and ventral
`parts); b = nail bed; c = hyponychium ('sole horn').
`
`eponychium lies the matrix which may be divided into a superficial proximal
`and a deeper distal part. This topographical relation is clinically important as
`the superficial part of the matrix may be involved in diseases of the proximal
`nail wall.
`Distal to the matrix lies the nail bed with its two sections, the hyponychium
`and the 'sole horn ' (in English nomenclature, 'hyponychium' refers to the 'sole
`horn' only). The hyponychium is connected to the underlying corium by capil(cid:173)
`lary-rich longitudinal corrugated ridges of epithelium, whereas the narrow termi(cid:173)
`nal 'sole horn' possesses the normal papillary structure of the dermo-epidermal
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`Runne/Orfanos
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`104
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`Fig. 4. NaIl ,urface, growth dlIection from up to down. Scanning electron micograph.
`Fig. 5. Free naIl border. Scanning electron micrograph.
`
`border. Matrix and connective tissue of the nail bed are without subcutis and are
`directly attached to the end phalanx. In the region of the 'yellow line' the nail
`plate becomes detached from its substratum. The resultant cleft is made water(cid:173)
`tight by the 'sole horn'.
`The matrix produces the cells of the nail plate and so does the nail bed,
`although to a small extent only. Both keratinize in the manner of parakeratosis
`without the formation of keratohyalin (79b, 80, 96a, 226). Eponychium and
`'sole horn', however, show normal epidermal keratinization. As the matrix con(cid:173)
`tains melanocytes in the lower 2-4 cell layers (86), the nail plate may be pig(cid:173)
`mented to a varying degree depending on race.
`The nail bed contributes a few cornified cell layers to the underside of the
`nail. Production and apposition of the nail bed keratin follow synchronously
`with the extension of the nail plate. Clinically, the nail bed does not possess
`movement of its own (227), yet autoradiography demonstrated at least the wan(cid:173)
`dering of a few matrix cells into the nail bed (139). As for the rest, the nail bed
`serves as a slide and holder of the nail plate.
`The nail plate itself consits of adherent, dead and largely denucleated cells.
`whose cell borders, in contrast with hair, are retained. Ultrastructurally, the nail,
`like hair and epidermis, contains keratin of the alpha type. In cross section the
`nail cells form compact horizontal horn cell lamellae. At the nail surface the nail
`cells slant from proximal-dorsal to distal-volar and cover each other, overlapping
`like roof tiles (fig. 4). Only at the free border where the intercellular cement is
`partially removed by detergents or other noxious influences, do the nail cells
`diverge (fig. 5).
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`The Human Nail
`
`105
`
`Dorsal nai l
`
`-Intermediate nail
`
`Ventral nail
`
`Dorsal
`
`Jentral
`
`Matrix
`
`all bE-O
`
`Fig. 6. Origin and arrangement of the three layers of the nail plate.
`
`The nail plate itself, 0.5 mm thick, consists of three layers. Two are derived
`from the matrix and the third from the nail bed. All three differ in structure and
`histochemical properties (2, 65, 79b, 80, 96a, 112, lIS). The dorsal layer (,dorsal
`nail') arises from the dorsal matrix and consists of hard keratin, only a few cell
`layers thick. The middle layer (,intermediate nail'), three-quarters of the whole
`nail thickness, is fOimed by the large ventral matrix and consists of softer kera(cid:173)
`tin. The dorsal and intermediate nails form the greater part of the nail, the so(cid:173)
`called hard nail. The nail bed adds a one or two cell-layer thick ventral layer
`('ventral nail'), consisting of soft hyponychial keratin, to the existing hard nail
`(lIS) (fig. 6). The ventral nail also grows on its own, e.g., after nail extraction,
`covering and protecting the nail bed.
`The activity of the nail bed in nail cell formation is very limited - as far as
`has been observed in autoradiographic investigations in apes (233). However, the
`ventral nail has a special function in that it connects the nail plate firmly with
`the substratum. For that reason considerable force is needed to remove the nail
`and with it the nail bed epidermis. Many pathological changes such as pachy(cid:173)
`onychia, subungual keratoses and onycholysis occur in the hyponychial keratin.
`
`2. Chemical and Physical Properties
`
`Chemically the nail plate consists mainly of keratin, a scleroprotein contain(cid:173)
`ing high amounts of sulfur. The amino acid content corresponds largely to that
`of hair; on the other hand, it differs from the keratin of the stratum corneum.
`Glutamic acid, cystine, arginine, serine and leucine are present in higher amounts
`(72, 109). The lipid content lies below 5%, sulfur at about 4(;;:. Ca, Mg, Zi, Fe
`and Cu are only present in trace amounts (46,214) and are presumably of no
`significance to the hardness of the nails.
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`Runne/Orfanos
`
`106
`
`In these investigations one should always consider the environmental and
`endogenous influences which may be taken up by the nail surface. In muco(cid:173)
`viscidosis (,fibrocystic disease') the sodium content of the nails is increased and
`nail material may be used for diagnostic purposes (74, 10Sa).
`The nail contains about 18% water. As the diffusion-constant of water is
`about 100 times greater than that of the stratum corneum, the nail plate swells
`easily and is as porous as hair. If the water content rises to 30%, the nail be(cid:173)
`comes opaque and soft; if it falls below 16% the nail becomes brittle (174)
`(see S.3.2.). A curious fact is that in spite of the absence of sweat glands, the
`water loss in the form of insensible perspiration per unit surface area of nail is as
`high as that of the palms and thus more than most other body regions (39,93).
`With the help of standardized determination of the swelling properties
`of the nail in sodium hydroxide solution, Zaun (236, 237) and Zaun and Becker
`(238) showed that the tendency for swelling is decreased in psoriatic and dys(cid:173)
`trophic brittle nails and in the nails in the yellow nail syndrome. Hence, a
`decrease in swelling capacity seems to point to abnormally produced nail ma(cid:173)
`terial. In contrast, the rate of swelling of nails loosened by the action of fungi
`was much increased. The decreased swelling capacity could frequently be re(cid:173)
`stored to normal by therapeutic regimes with gelatin-vitamin A.
`It is now generally accepted that the hardness of the nails depends on the
`arrangement, and close attachment of the nail cells to each other. The transverse
`orientation of the keratin filaments to the direction of growth and the presence
`of intercellular cement are both factors of considerable importance (26, 63, 65).
`Curiously, the nails in patients suffering from protein deficiency appear to be
`harder than those in healthy patients (I 64b).
`The chemical analysis of nail substance has forensic importance. Even after
`several months it is often possible to give a correct estimation of the type of
`toxin and when it was ingested. The nail of the big toe is the preferred site of
`investigation because of its size and slowness of growth. While such determi(cid:173)
`nations are, in principle, also possible in hair, the data acquired from the nails
`are more reliable (7Sa, 83). Moreover, blood groups may also be demonstrated in
`the nail substance. This will be important in forensic medicine, if only hands or
`feet are obtainable or if mummification or putrefaction have set in (7Sc).
`
`3. Embryology
`
`The development of the nail starts in the 10th embryonic week with a
`thickening of the epidermis of the dorsal end phalanx (so-called primary nail
`field). At the level of its proximal transverse groove, an epidermal duplication
`grows and forms the primordial matrix (fig. 7). Before this matrix begins defini(cid:173)
`tive nail production, a thin, rootless forenail arises from the subsequent 'sole
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`The Human Nail
`
`107
`
`a
`
`b
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`Fig. 7. Embryological development of the nail. a 10th week. b 16th week.
`
`horn' area. The forenail covers the whole nail bed until the 14th week (226).
`Meanwhile, the primordial matrix differentiates and produces the nail plate. The
`protruding nail finally pushes through the eponychium and covers the entire nail
`_
`bed by the 17th week.
`Initially, matrix and nail bed keratinize similarly to the normal epidermis
`with the formation of keratohyalin (80); in both areas typical parakeratotic
`keratinization follows at a later stage (226). However, the 'sole horn' does not
`follow this pattern. In the fifth month dorsal and intermediate layers are already
`distinguishable in the nail plate. The ventral layer only appears at the end of the
`fetal period.
`
`4. Growth
`
`The matrix forms the nail continuously and not cyclically as in the case of
`hair. This avoids alternating cycles of growth and loss of nails. The direction of
`growth is determined by the special arrangement of the matrix cells (80) and
`the protecting eponychium (102) which, together with the nail bed, serves as a
`guiding slide. However, if part of the matrix is dispersed by trauma, the nail
`grows upwards in an uncontrolled manner (168a).
`The growth rate of the fingernails is on average 0.1 mm/day or 3 mm per
`month (56, 88, 97, 104, 149, 153, 154, 195). Hair grows three times as fast
`(0.35 mm/day). The growth rate is determined by the turnover of the matrix
`cells; the thickness of the nail, however, by the number of dividing matrix cells,
`i.e., by the matrix volume. Whereas the senile nail grows more slowly and be-
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`Runne/Orfanos
`
`108
`
`Table I. PhysIOlogical vanatlOns of naIl growth
`
`t aster growth
`
`Slower growth
`
`fingernails
`middle fingers
`dominant hand (i.e. rights vs. left)
`day
`summer
`in 2nd and 3rd decade
`men
`
`toenaIls
`thumbs and little fingers
`non-dommant hand (i.e., right vs. left)
`night
`wmter
`before 3rd decade and after the age of 50
`women
`
`comes thicker at the same time, the growth rate and thickness of the nail are in
`general not correlated (76).
`Physiological variations in growth rate exist even in the individual (table I).
`The toenails grow 30-50% slower than the fingernails (152), and there is a
`definite order among the fingers: the longer the finger, the faster the growth,
`i.e., in order of the fingernails 3-2-4-1-5 (51,104,149). In addition, there is
`an age dependence. The highest growth rates (0.123 mm/day) were found be(cid:173)
`tween 15 and 30 years of age, and the lowest (0.06-0.09 mm/day) before the
`3rd and after the 50th year. In general, the rate of linear nail growth decreases in
`the course of life by 50% (31, 104, 140b).
`Other factors, partly pathological, influence nail growth either positively or
`negatively (table II) (31, 54a, 84, 205). For example, in psoriasis, besides epider(cid:173)
`mal hyperproliferation, nail growth is also accelerated: this acceleration is greater
`in psoriatic than in the clinically normal nails. While methotrexate and azathio(cid:173)
`prine inhibit the accelerated nail growth, it remains unchanged by systemically
`administered corticosteroids (51, 53). On the other hand, severe general diseases
`can slow down nail growth or temporarily stop it completely. Denervation will
`also decrease the growth velocity.
`Acceleration of pathologically diminshed nail growth may be attained by
`the use of gelatin, cystine methionine and high doses of biotin (95, 104,220).
`Treatment of Parkinson patients with I--dopa is said to accelerate the growth of
`their nails (132).
`The regeneration time of the nail is also dependent on the growth rate. Fur(cid:173)
`ther, after extraction, it is possible for the thickness of the nail to show a tempo(cid:173)
`rary fluctuation (25). In nail extraction the matrix loses only its superficial layers
`and then carries on its continuous production of nail keratin. However, a finger(cid:173)
`nail takes about 40 days to emerge from the nail fold, and growth to the finger(cid:173)
`tip takes another 120 days. The total regeneration time is 160 days (fig. 8). For
`the toenails, regeneration time amounts to about I year. Treatment of nail
`diseases therefore always demands long periods of time.
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`The Human Nail
`
`109
`
`Table II. Influences on growth ra te of nail
`
`Growth accelerating
`
`Growth slOWing
`
`General factors
`hyperemia
`
`onychophagia, piano playing
`
`nail extraction
`onycholysis
`pregnancy
`
`Systemic and skin diseases
`psoriasIs
`congemtallchthyosiform erythroderma
`pityriasis rubra pilaris
`dermatitis herpetiformis
`paronychia
`hyperthyroidism
`Drugs
`gelatin, biotin, cystine and methionine,
`I.-dopa
`
`General factors
`circulatory disorders, arterial and venous
`matrix lesIOn due to trauma,
`radiation or nerve injury
`
`lactation
`
`Systemic and skin diseases
`chronic eczema
`congenital pachyonychia
`nail-patella syndrome
`yellow nail syndrome
`Infectious diseases
`hyperthyroidism
`Drugs
`cytostatic drugs
`
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`hyperthyroidism
`hyperthyroidism
`
`hyperthyroidism
`
`hyperthyroidism
`
`V,s,ble
`nail
`
`12mm
`
`Covered 14 mm
`
`matnx
`
`Fig. 8. NaIl regeneratIon tIme.
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`Runne/Orfanos
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`110
`
`Table III. Pathological changes of the nail organ and their causes
`
`Congenital
`
`AcqUlred
`
`Isolated nail changes
`anonychia, micronychia
`kOilonychia, platonychia
`leukonychia
`tcnms racket nail
`onychogryposis
`ptergyglUm
`As concomitant symotom in skin diseases
`congemtal pachyonychia
`bullous congenital ichthyosis
`daner'.; disease and other
`uncommon genodermatoses
`acrodermalltls enteropathica
`nail-patella syndrome
`syphlhs
`epidermolYSIS bullosa
`
`Skin diseases
`psoriasis, eczema, alopecia areata
`and many other skin conditions
`fungal and candidal mfectlOns
`bacterial mflammatlOns
`tumors
`
`Systemic diseases
`mfectlOus diseases
`cardiac, circulatory and pulmonary
`disorders
`renal insufficiency, hver cirrhoSiS
`anemia, diabetes
`Drugs and toxins
`atabnn, chloroquine, silver
`mercury, phenolphthalem
`cytostalic drugs, arsemc, thallium
`photosensltlzers
`Exogenous factors
`trauma and nervous habit
`occupational and cosmelic mt1uenccs
`X-rays
`
`For the same reason all nail changes due to matrix Injuries only become
`visible after a latent period of some weeks. The slowly appearing leSIOn then
`reveals the history, duration and extent of the preceding lesion.
`
`5. Pathological Changes
`
`5.1. General Principles and Types of Lesions
`
`Nail changes may be congenital or acquired. They may be Isolated or a
`symptom of another disease. The acquired lesions, which are of more impor(cid:173)
`tance in clinical practice, are mostly the effect of skin or systemic disease, drug
`damage or exogenous factors (table III). Many nail diseases occur as both con(cid:173)
`genital and acquired conditions, i.e., anonychia, koilonychia, leukonychia and
`onychogryphosis.
`Every single part of the nail - matrix, bed, wall and plate - can be damaged
`and can react, producing specific signs. All kinds of damage can affect the
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`The Human Nail
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`111
`
`Fungi, bacteria and candida,
`trauma, chemical noxes
`
`pharmacological effects,
`pharmacological effects,
`
`Dermatit is, bacterial and
`candida Infections, tumors
`trauma, chemical noxes
`
`Polyetiology
`(psOriaSIS, eczema, mycOSIS,
`tumors, general diseases,
`IrradiatIOn)
`trauma, chemical noxes,
`IrradiatIOn)
`IrradiatIOn)
`
`pharmacological effects,
`pharmacological effects,
`
`PsoriaSIS, sP'Jere general diseases,
`drugs, tumors, ChroniC dermatitis,
`trauma
`
`Fig. 9. Pnmary site of typical damage caused by the leSion on the nail.
`
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`matrix and nail bed (e ,g., skin diseases, tumors , pharmacological effects, serious
`systemic diseases and trauma), whereas the nail wall and nail plate are especially
`prone to lesions due to animate or inanimate exogenous stimuli (fig. 9). The
`resulting types of lesions are likewise most variable in the region of the matrix
`and nail bed, whereas the nail wall and plate possess only a limited number of
`responses (fig. 10).
`It is interesting to note that changes in the matrix from congenital disorders,
`systemic diseases of drugs usually damage all the nails whereas lesions due to skin
`diseases and exogenous factors are as a rule restricted to single nails . Corresponding
`to nail formation, the dorsal layer of the nail is involved in lesions of the dorsal
`matrix, whilst the intermediate layer is affected by lesions of the ventral matrix .
`Damage to the nail bed becomes evident in the ventral part of the nail and its
`connection with the nail bed .
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`Runne/Orfanos
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`112
`
`Discoloration, dlsformatlon,
`onychoschlslS, onychorhex ls, onycholysIs
`
`pharmacological effects,
`pharmacological effects,
`
`Paronychia, hang nalls,
`Ingrowing nail, pterygium
`
`.....J
`<!
`Z
`
`Oil patch, discoloration
`subungual keratosIs,
`onycholYSIs, brittleness,
`pachyonychia
`
`o
`w
`CD
`
`<!
`Z
`
`pharmacological effects,
`pharmacological effects,
`
`Aplasia, atrophia, hypertrophla,
`changes In shape, brittleness,
`transverse grooves, ridges,
`fissures, Beau's lines,
`onychomadesIs
`
`Fig. 10 Type, of lesIOns and results of damage on the nail.
`
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`While not every injurious influence leads to a characteristic lesion, most
`types of lesions make it possible to draw conclusions as to the site and nature
`of the lesion. In generaL changes of the nail surface and thickness are due to
`a disturbance of the matrix. However, other symptoms may remain inconclu(cid:173)
`sive; e.g. , discoloration may be due to changes in the matrix or the nail bed as
`well as the intact nail plate (fig. 10).
`Many diseases and injuries involve several parts of the nail at the same time .
`The sum of the symptoms may thus lead to a definite diagnosis. For example,
`in the psoriatic nail, oil patch, subungual hyperkeratoses and pitting occur
`simul taneously.
`We will now discuss the pathological nail changes in relation to their clinical
`symptoms as observed by the physician during his examination.
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`The Human Nail
`
`5.2. Changes of Nail Bulk
`
`113
`
`5.2.1. Formation and Size
`In the various forms of anonychia the nail plate is absent. The rare congeni(cid:173)
`tal nail aplasia (anonychia aplastica) is due to a growth impairment of the matrix
`and may be accompanied by other defects such as skin aplasia, poikiloderma,
`leukoplakia, congenital deafness and epidermolysis bullosa (fig. 11) (61, 142,
`177a, 216). It is also seen in consanguinity (90).
`In acquired nail atrophy (anonychia atrophica) there is restriction or even
`cessation of matrix division due to serious inflammatory or traumatic damage.
`Examples are epidermolysis bullosa dystrophic a , severe injuries, lichen planus
`(fig. 12) (19, 125, 127, 230) and, in exceptional cases, in severe disturbances of
`the circulation, following gold therapy or in Stevens-Johnson syndrome (218,
`219). Irreversible nail loss with scar formation is the result.
`This is in contrast to the unusual form of aplasia keratodes in which, instead
`of the matrix, a metaplastic squamous epithelium is formed that only produces
`loose horn masses (12).
`In addition to these irreversible forms, anonychia may occur temporarily,
`e.g., after nail loss due to an illness or to (traumatic or iatrogenic) nail removal
`(168a) (see 5.2.2. and 5.6.4.). In permanent anonychia the proximal nail wall
`frequently grows forwards like a pterygium, covering the whole nail bed (fig. 15).
`Hypoplasia of the nail plate (micronychia) may point to the autosomal(cid:173)
`dominant inherited nail-patella syndrome. In such cases the ulnar part of the
`thumbnail is usually involved. The other nails may also be involved but to a less(cid:173)
`er extent (fig. 13). The lunula often has an elongated, triangular shape. In these
`patients we also find hypoplasia and subluxation of the patella and head of the
`radius, exostoses of the os ileum and chances of the glomerular membrane wi th
`symptoms of chronic glomerulonephritis (33, 119). Other anomalies such as
`cutis laxa may also occur and the syndrome should perhaps be considered as a
`general dysplasia of connective and supporting tissues.
`Likewise, in yellow nail syndrome nail growth is restricted and may cease
`altogether. In most cases thumb and index finger show more changes than the
`other fingers (see 5.7.6.).
`The embryopathic hydantoin syndrome shows a characteristic hypoplasia
`of the fingernails, terminal phalanges of the fingers and sometimes the toes. It
`is seen in children whose mothers were on protracted hydantoin therapy during
`the first months of pregnancy (110).
`Finally, hypoplasia of the nails is also found in ectodermal dysplasia of the
`hidrotic type (204).
`In patients with congenital onychodysplasia of the index finger (99), various
`findings such as anonychia, micronychia and polyonychia may be combined.
`Only the nails of the index fingers are involved. There is no familial occurence.
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`In contrast, in onychophagia and in mechanical overstimulation an artificial
`shortening of the nails can be seen.
`Poly onychia and macronychia, both rare disease, are mostly congenital
`(217). Polyonychia may also be acquired due to traumatic splitting of the matrix
`(168a) and macronychia may be due to acromegaly. Heterotopic nails (206) are
`extremely rare.
`
`5.2.2. Nail Loss
`Loss of the nail may be caused by damage to the matrix (onychomadesis),
`to the nail bed (total onycholysis) or by exegenous factors. In onychomadesis
`the nail loosens itself from its base as a result of damage to the matrix (5). The
`nail plate may be lost through trauma, intensive X-ray therapy (8), serious
`general diseases or, in rare cases, through idiopathic causes. This kind of nail
`loss is usually reversible. Even periodic nail loss may occur, apparently as part of
`epidermolysis bullosa (123).
`In latent onychomadesis the nail plate shows a transverse, split-like interrup(cid:173)
`tion which is likewise due to a transient complete cessation of matrix activity.
`However, the nail is retained because its distal parts is still connected to the
`nail bed (fig. 14). This change is seen in general acute diseases, bacterial parony(cid:173)
`chia, matrix inflammation or vesicular dermatoses such as bullous pemphigoid,
`Lyell or Stevens-Johnson syndromes. The transverse split becomes visible only
`after the usual latent period (cf. ref. 4 and fig. 8). Therefore, it is possible to
`make deductions regarding the point in time and the degree of the damage.
`A different mechanism is seen in onycholysis totalis, in which the nail is
`detached from the nail bed by injury and is lost (see 5.6.4.). One should distin(cid:173)
`guish this condition from onychotillomania, which is usually restricted to the
`little finger (fig. 15).
`
`5.2.3. Nail Thickness
`A thickening of the nail plate above its normal 0.5 mm may be caused by
`the matrix (nail hypertrophy) or the nail bed (pachyonychia). Hence, nail
`hypertrophy is a function of the matrix. Hypertrophic nails are seen as develop(cid:173)
`mental anomaiJes, in ichthyosis congenita, psoriasis. pityriasis rubra pilaris,
`Darier's disease and most commonly 10 posttraumatic conditions. We have
`also observed it in melanotic erythroderma (fig. 16). Finally, hypertrophiC nails
`may change into a claw-Ilail (fig. 17) and ollychogryposis in which thickening
`and torsion are usually caused by chronic trauma. e.g .. pressure of the shoe on
`the nail of the big toe. Under the microscope the cells of such nails show a
`disorderly, wave-like distribution with hyperchromatism. parakeratosis and
`numerous splits (5).
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`Fig. 11. CongenItal absence of the nail plate In epldermolY~ls bullo~a.
`Fig. 12. Acquired anonychia In lichen planm.
`Fig. 13. Th umbnalls In nail-patella syndrome.
`Fig. 14. Latent onychomadesIs after Stevens-Johnson ~yndrome.
`Fig. 15. Onychotillomania. PterygIUm formation on the nght httle finger. Two of the
`phalanges had to be amputated because of self-muttiatlOn.
`Fig. 16. Natlhypertrophy In melanoerythrodcrma.
`
`J
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`J
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`5
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`Fig. 17. Onychogrypo~ls in a patient wIth schizophrenia.
`Fig. 18. PachyonychIa congenita with palmar hyperkeratoses.
`
`Thickened nails with increased transverse curvature are likewise seen in the
`yellow nail syndrome (see 5.7.6.), watch-glass nail and in clubbing (see 5.4.).
`Unlike the nail hypertrophies, the pathological changes in pachyonychia are
`exclusively localized in the nail bed. In pachyonychia congenita the ventral nail
`is markedly thickened by an increase in the hyponychial keratin (64, 168d),
`while the so-called hard nail plate remains unchanged (fig. 18). Compact masses
`of subungual keratin, a few millimeters high, adhere to the nail plate and arch it
`upwards, so that its form becomes convex. Usually, a crescent-shaped cavity is
`formed between the nail plate and nail bed. The same mechanism occurs in
`response to nail bed involvement by psoriasis, chronic eczema and mycoses.
`An increased amount of amorphous PAS-positive material is seen (6). We have
`also observed an acquired pachyonychia in erythrodermic actinic reticuloid
`(fig. 19).
`Thin nails are due to a decreased matrix volume, whether by diffuse matrix
`atrophy, a reduction in the length of the matrix or the loss of a matrix segment.
`Such changes occur as developmental defects, in iron deficiency anemia, periph(cid:173)
`eral circulatory disturbances, epidermolysis bullosa and sometimes in lichen
`planus (127). We have observed thin, soft nails in a very severe form of endoge(cid:173)
`nous eczema (fig. 20). Finally, in platonychia and koilonychia the nails are also
`thin (see 5.4.).
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`19
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`20
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`Fig. 19. Acquired pachyonychia in erythrodermic actinic reticulOld.
`Fig. 20. Thin soft nail with longitudinal ridges in a severe case of atopic dermatitis.
`
`5.3. Changes in Quality
`
`5.3.1. Soft Nails
`An extremely wft and at the same time often brittle nail plate (hapalonychia)
`can be congenital or acquired . The so-called soft nail disease is- based on a con(cid:173)
`genital matrix defect (159). In acquired forms, general disease including cachexia,
`peripheral circulatory disorders and occupational contact with water and chemi(cid:173)
`cals (petrol, stain remover, alkalies) may be the cause. In koilonychia the nails
`are also generally softer (see 5.4.).
`For therapeutic purposes nails can be softened by an application of potas(cid:173)
`sium iodide in lanolin under a polythene dressing, while the surrounding skin is
`covered with zinc ointment. The softening is so intense that after a few days the
`nails may be cut to a third of their size quite painlessly (187). Another nail
`softener is local application of high concentrations of urea in Lassar's paste in
`various modifications, as has been introduced by Farber.
`
`5.3.2. Brittle Nails
`Brittle, slightly transparent nails (onychorrhexis) may be due to a protracted
`disease of the total matrix or to damage of the completed nail plate. Chronic
`inflammation, extensive keratinization disturbances (psoriasis, eczema, lichen
`planus, ichthyosis, Darier's disease) and peripheral circulatory disturbances,
`hypochromic anemia, myxedema and hypoparathyroidism have their effect on
`the matrix (fig. 20). Very grave diseases may lead to the so-called crumbling nail
`(fig. 21).
`A peculiar nail dystrophy, which clinically resembles a mycosis or psoriasis,
`is seen in gout. Longitudinal striations, brittleness and crumbling of the nail
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`Fig. 21. Crumbling nail in psoriasIs.
`Fig. 22. Onychopathia in gout.
`
`plate can be seen (fig. 22) (71, 160). Such 'gout nails' are of diagnostic impor(cid:173)
`tance in atypical joint diseases.
`In the Cronkite-Canada syndrome (intestinal polyposis with malabsorption),
`a marked dystrophy of fingernails and toenails with synchronous yellow discolora(cid:173)
`tion is observed in addition to diffuse alopecia and pigmentation disorders (144).
`In old age the nail becomes increasingly brittle and fragile.
`In the majority of adults with brittle nails there is a secondary loosening of
`the nail structure, often caused by contact with acids, alkalies, solvents, nail
`polish remover or detergents. The combined effect of repeated absorption of
`water by the nail in humid envi