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Hypomelanosis of Ito: electron microscopical observations on two new cases
JOURNALOF
Dermatological Science
ELSEVIER
Journal of Dermatological Science 13 (1996) 87-92
Short communication
Hypomelanosis of Ito: electron microscopical observations on two new cases V. Cavallari”, A.F. Ussia”, M. Siragusab, C. Schepisb,* “Laboratory
of Electron Microscopy, Department of Human Pathology, bUnit of Dermatology, Oasi Institute [IRCCS],
University of’ Messina, Messina, Italy Troina, Italy
Received 5 June 1995; revised 27 November 1995; accepted 30 November 1995
Abstract An ultrastructural study on two new cases of Ito’s hypomelanosis is reported. According with previous studies on this pathological condition, a marked reduction of melanocytes is detected in the hypopigmented areas. In the proximity of preserved melanocytes, a nearly normal content of melanosomes is detected in basal keratinocytes. Melanocyte profiles are frequently located in close relationship with the basal lamina. An apparent increase of nerve endings is demonstrated at the dermo-epidermal edge. Nerve fibres show no pathological alterations. A functional impairement of the melanocytes is hypothesized, involving regressive changes and a tendence towards a round shape of their profiles. This could in part account for the prevalent basal location of the melanocytes. The role of the dermal nerve endings in the pathogenesis of the hypopigmented lesions is discussed. Keywords:
Hypomelanosis
of Ito; Ultrastructure;
Blaschko’s lines
1. Introduction The neurocutaneous syndrome called hypomelanosis of Ito (HI) shows ipo-achromic macules which follow prevalently Blaschko’s lines. A consistent association with eye, neurological and skeletal abnormalities is reported [ 1,2].
* Corresponding author, Unit of Dermatology, Oasi Institute for Research on Mental Retardation and Brain Aging (IRCCS), Via Conte Ruggero 73, 94018 Troina (EN), Italy. Tel.: + 39 935 653986: fax: + 39 935 653660.
The hypocromic lesions are observed at birth or within the first two years of life [2]. Seizure disturbances and mental retardation are the most common CNS symptoms. Scoliosis and finger deformities are also frequently observed. The diagnostic criteria of Ito’s hypomelanosis were suggestedby Ruiz-Maldonado et al. in 1992 [2]. The authors invoke the presence of the cutaneous abnormalities (‘sine qua non criterion’) associated with one or more ‘major’ symptoms consistent with CNS or musculo-skeletal involvement.
0923-181l/96/$15.00 G 1996 Elsevier Science Ireland Ltd. All rights reserved SSDI 0923-1811(95)00507-2
The ultrastructural reports on HI point out structural abnormalities of melanocytes such as loss or numerical reduction of melanosomes (frequently smaller than expected) and regressive changes. An increase in nerve endings (unmyelinated axons surrounded by Schwann cells) in close proximity with the basal layer of the epidermis was reported by Morohashi et al. [3] in the hypopigmented zones. A case report of HI was recently reported by our group [4]. Here we report further ultrastructural observation on two new cases. 2. Materials
and methods
Two additional cases of HI were diagnosed according to the Ruiz-Maldonado’s criteria. Both subjects were Caucasian females aged 16 and 19 years, respectively. The first one showed non-symmetrical hypopigmented streaks on the back, on the toraco-lumbar area, and a whorl on the right abdominal region. She presented mental retardation, microcephaly, short stature, hypertelorism and several skeletal anomalies. The second one presented hypopigmented lesions arranged in streaks along Blaschko’s lines, mainly evident on the right arm, buttock and leg. Mental retardation and kyphoskoliosis were also detected. An informed consensus for the skin biopsy was obtained from the parents. Punch biopsies were collected from the involved areas. Tissue fragments were immediately fixed by immersion in modified Karnovsky’s fluid containing 3% glutaraldehyde and 2% paraformaldehyde (4°C pH 7.2). After 3 h, fragments were repeatedly rinsed with cold Soerensenbuffer (0.1 M, pH 7.4) containing saccarose 0.66 M, post-fixed in buffered 1% osmium tetroxide (0.1 M, pH 7.4), dehydrated in scalar dilutions of ethanol, treated with propylene oxide and embedded in epoxy resin (Durkupan Fluka). Thick sections were obtained with glass knives and stained with toluidine blue. Thin sections (approx. 600 A) were obtained with diamond knives and counterstained with uranyl acetate and lead citrate. Section were
viewed on the electron microscope Siemens 102 operating at 80 KV. 3. Results
No peculiar findings were detected on thick sections. The basal keratinocytes appeared hypopigmented, and an apparent numerical reduction of melanocytes could be suggested (Fig. 1). At the electron microscope, the first finding was the detection, in both cases, of a non-homogeneous distribution of the hypopigmentation. Large areas almost completely devoid of melanosomes alternated with areas showing an nearly normal content of melanosomes in the keratinocytes. A more careful observation demonstrated the presence of clusters of normally pigmented keratinocytes in association with a normally-looking melanocyte. A few micrometers away, keratinocytes completely devoid of melanosomes were present. In such regions, an increase of profiles of Langerhans cells was frequently associated with the presence of lymphocytes with indented nuclei lying among the keratinocytes. In Case 2, an addional pathological change was found: profiles of melanocytes showing regressive alterations (i.e. a marked vacuolization) were found in close proximity with keratinocytes showing similar regressive changes (Fig. 2). In these cells, melanosomes were arranged in aggregates surrounded by a unit membrane. A neighbouring keratinocyte profile is completely devoid in melanosomes (Fig. 2, inset). Intercellular spaces were apparently dilated, and occasional acantolysis was observed in association with lymphocyte profiles. In the hypopigmented areas the melanocytes showed slight regressive changes. An interesting finding is the apparent increase of the melanocyte surface directly faced with the basal lamina. No structural alterations were detected in the dermis except occasional lymphocyte perivascular infiltrates. A rich nervous network made mainly of unmyelinated axons was observed in the papillary dermis (Fig. 3). Nerve fibres did not show structural abnormalities and were regularly surrounded by normally-looking Schwann cells.
V. Cavallari
et al. /Journal
of Dermatological
Science 13 (1996) 87-92
Fig. I. Basal keratinocytes. The number of melanosome profiles is reduced. An unmyelinated mal junction (uranyl acetate and lead citrate, x 15 000).
89
nerve bundle lies at the dermo-epider-
90
V. Cavallari
et al. /Journal
of’Dermatologica1
Science 13 (1996) 87-92
Fig. 2. Regressive changes of melanocytes and keratinocytes. A melanocyte profile with increase of cytoplasmic organelles and ninent vacuolization is associated with keratinocyte profiles containing melanosome aggregates. A neighboring keratinc xyte ibot tom right) is devoid of melanosomes ( x 8000). Inset: a detail of an intercellular contact showing the complete segregatic m of mosomes in the cytoplasm of a keratinocyte ( x 20000).
V. Cavallari
et al. 1 Journal of Dermatological
Science 13 (1996) 87-92
91
Fig. 3. (a) Nerve fibers in the dermis. An unmyelinated axon in close relationship with the basal keratinocytes ( x 10000). (b) A melanocyte apparently protruding in the dermis ( x 12000).
92
V. Caoallari et al. I Journal
of Drrmatological
4. Discussion
A functional abnormality of melanocytes is generally accepted in HI. A disorder of the melanocyte metabolism involving the selective suppression of the eumelanin synthesis was recently demonstrated in HI IS]. In the two cases reported here the differential diagnosis was made against the other linear and whorled pigmentations, i.e. nevus depigmentosus, incontinentia pigmenti, linear and whorled nevoid hypermelanosis [6,7]. The morphological findings confirm the previously reported observations [S- lo]. In particular, the apparent correlation of the hypopigmentation with a local loss of functioning melanocytes is confirmed in our observations. Normally pigmented keratinocytes can be detected in relation with preserved melanocytes, whereas in the hypopigmented zones no melanocytes were found. In agreement with other ultrastructural observations [3], an apparent increase in nerve endings was observed in the two new casesdescribed here. These peripheral nervous structures did not show pathological changes. The role of the dermal nerve fibres in the regulation of the pigmentation was not sufficiently explored. It is conceivable that neurotransmitters could act on the phenotypic expression of the various cells lying in the dermoepidermal microenvironment. An increased melanogenesis can be a non-specific consequence of a pathologic process involving the production of inflammatory release factors proved to stimulate the nerve endings. On the other hand, hypopigmentation can be observed in denervated cutaneous areas in association with other hypotrophic changes of the skin and annexes. Therefore, we could suggest that Ito’s linear and whorled hypopigmentation is an inhibitory signal carried by the nerve endings. The regressive changes of melanocytes associated with similar changes of the neighbouring keratinocytes were found only in one case. This could reflect an early stage in the pathogenesis of the hypopigmented lesions, whereas in the majority of fields the melanocyte profiles are simply absent.
Science 13 (1996) 87-92
The frequent appearance of the melanocytes in close relationship with the basal lamina, and, occasionally, the apparent protrusion of parts of cytoplasm towards the dermis is difficult to explain. This arrangement is infrequent in normal skin biopsies, where the melanocyte profiles are regularly spaced. However, in conditions involving a functional activation and/or a numerical increase of melanocytes, the probability of finding contacts with the basal lamina is increased. In our experience, melanocyte profiles are seen prevalently surrounded by keratinocytes. Contacts with the basal lamina involve only a limited amount of the cell surface. Regressive changes of melanocytes, a reduction of the cytoplasmic processes and a tendency towards a circular contour could account in part for their basal location.
References [I] Castroviejo IP, Lopez-Rodriguez L, Medina MC, Salamanta-Maesso C, Roche-Herrero C. Hypomelanosis of Ito. Neurological complications in 34 cases.Can J Neurol Sci 15: 124-129, 1988. [2] Ruiz-Maldonado R, Toussaint S, Tamayo L, Laterza A, del Castillo V. Hypomelanosis of Ito: diagnostic criteria and report of 41 cases. Pediatr Dermatol 9: I-IO, 1992. [3] Morohashi M, Hashimoto K, Goodman TF, Newton DE, Rist T. Ultrastructural studies of vitiligo, Vogt-Koyanagi syndrome, and incontinentia pigmenti achromians. Arch Dermatol 113: 7555766, 1977. [4] Schepis C, Cavallari V, Elia M, Ussia AF, Pontieri F. Hypomelanosis of Ito: ultrastructural study. Eur J Pediatr Dermatol 2: 115-120, 1992. [S] Fukai K, Ishii M, Wakamatsu K, lto S, Sakamoto H, Fujiwara H, Ohno A, Hamada T. Selective decrease of eumelanin in hypopigmented epidermis of hypomelanosis of Ito. Pediatr Dermatol I I: 261-263, 1994. [6] Harre J, Millikan LE. Linear and whorled pigmentation. Int J Dermatol 33: 529-537, 1994. [7] Schepis C. Congenital or perinatal macules distributed according the Blaschko’s lines. Eur J Pediatr Dermatol 4: 73-75,
1994.
Grosshans EM, Stoebner P, Bergoend H, Stall C. Incontinentia pigmenti achromians (ITO). Etude clinique et histo-pathologique. Dermatologica 1971; 142: 65-78 [9] Nordlund JJ, Klaus SN, Gino J. Hypomelanosis of Ito. Acta Dermatovener (Stockholm) 57: 261-264, 1977; [IO] Cambazard F, Hermier C, Thivolet J, Perrot H. Hypomelanose de Ito. Revue de la litterature a propos de 3 cas. Ann Dermatol Venereol 113: 15-23, 1986. [8]
Dermatological Science
ELSEVIER
Journal of Dermatological Science 13 (1996) 87-92
Short communication
Hypomelanosis of Ito: electron microscopical observations on two new cases V. Cavallari”, A.F. Ussia”, M. Siragusab, C. Schepisb,* “Laboratory
of Electron Microscopy, Department of Human Pathology, bUnit of Dermatology, Oasi Institute [IRCCS],
University of’ Messina, Messina, Italy Troina, Italy
Received 5 June 1995; revised 27 November 1995; accepted 30 November 1995
Abstract An ultrastructural study on two new cases of Ito’s hypomelanosis is reported. According with previous studies on this pathological condition, a marked reduction of melanocytes is detected in the hypopigmented areas. In the proximity of preserved melanocytes, a nearly normal content of melanosomes is detected in basal keratinocytes. Melanocyte profiles are frequently located in close relationship with the basal lamina. An apparent increase of nerve endings is demonstrated at the dermo-epidermal edge. Nerve fibres show no pathological alterations. A functional impairement of the melanocytes is hypothesized, involving regressive changes and a tendence towards a round shape of their profiles. This could in part account for the prevalent basal location of the melanocytes. The role of the dermal nerve endings in the pathogenesis of the hypopigmented lesions is discussed. Keywords:
Hypomelanosis
of Ito; Ultrastructure;
Blaschko’s lines
1. Introduction The neurocutaneous syndrome called hypomelanosis of Ito (HI) shows ipo-achromic macules which follow prevalently Blaschko’s lines. A consistent association with eye, neurological and skeletal abnormalities is reported [ 1,2].
* Corresponding author, Unit of Dermatology, Oasi Institute for Research on Mental Retardation and Brain Aging (IRCCS), Via Conte Ruggero 73, 94018 Troina (EN), Italy. Tel.: + 39 935 653986: fax: + 39 935 653660.
The hypocromic lesions are observed at birth or within the first two years of life [2]. Seizure disturbances and mental retardation are the most common CNS symptoms. Scoliosis and finger deformities are also frequently observed. The diagnostic criteria of Ito’s hypomelanosis were suggestedby Ruiz-Maldonado et al. in 1992 [2]. The authors invoke the presence of the cutaneous abnormalities (‘sine qua non criterion’) associated with one or more ‘major’ symptoms consistent with CNS or musculo-skeletal involvement.
0923-181l/96/$15.00 G 1996 Elsevier Science Ireland Ltd. All rights reserved SSDI 0923-1811(95)00507-2
The ultrastructural reports on HI point out structural abnormalities of melanocytes such as loss or numerical reduction of melanosomes (frequently smaller than expected) and regressive changes. An increase in nerve endings (unmyelinated axons surrounded by Schwann cells) in close proximity with the basal layer of the epidermis was reported by Morohashi et al. [3] in the hypopigmented zones. A case report of HI was recently reported by our group [4]. Here we report further ultrastructural observation on two new cases. 2. Materials
and methods
Two additional cases of HI were diagnosed according to the Ruiz-Maldonado’s criteria. Both subjects were Caucasian females aged 16 and 19 years, respectively. The first one showed non-symmetrical hypopigmented streaks on the back, on the toraco-lumbar area, and a whorl on the right abdominal region. She presented mental retardation, microcephaly, short stature, hypertelorism and several skeletal anomalies. The second one presented hypopigmented lesions arranged in streaks along Blaschko’s lines, mainly evident on the right arm, buttock and leg. Mental retardation and kyphoskoliosis were also detected. An informed consensus for the skin biopsy was obtained from the parents. Punch biopsies were collected from the involved areas. Tissue fragments were immediately fixed by immersion in modified Karnovsky’s fluid containing 3% glutaraldehyde and 2% paraformaldehyde (4°C pH 7.2). After 3 h, fragments were repeatedly rinsed with cold Soerensenbuffer (0.1 M, pH 7.4) containing saccarose 0.66 M, post-fixed in buffered 1% osmium tetroxide (0.1 M, pH 7.4), dehydrated in scalar dilutions of ethanol, treated with propylene oxide and embedded in epoxy resin (Durkupan Fluka). Thick sections were obtained with glass knives and stained with toluidine blue. Thin sections (approx. 600 A) were obtained with diamond knives and counterstained with uranyl acetate and lead citrate. Section were
viewed on the electron microscope Siemens 102 operating at 80 KV. 3. Results
No peculiar findings were detected on thick sections. The basal keratinocytes appeared hypopigmented, and an apparent numerical reduction of melanocytes could be suggested (Fig. 1). At the electron microscope, the first finding was the detection, in both cases, of a non-homogeneous distribution of the hypopigmentation. Large areas almost completely devoid of melanosomes alternated with areas showing an nearly normal content of melanosomes in the keratinocytes. A more careful observation demonstrated the presence of clusters of normally pigmented keratinocytes in association with a normally-looking melanocyte. A few micrometers away, keratinocytes completely devoid of melanosomes were present. In such regions, an increase of profiles of Langerhans cells was frequently associated with the presence of lymphocytes with indented nuclei lying among the keratinocytes. In Case 2, an addional pathological change was found: profiles of melanocytes showing regressive alterations (i.e. a marked vacuolization) were found in close proximity with keratinocytes showing similar regressive changes (Fig. 2). In these cells, melanosomes were arranged in aggregates surrounded by a unit membrane. A neighbouring keratinocyte profile is completely devoid in melanosomes (Fig. 2, inset). Intercellular spaces were apparently dilated, and occasional acantolysis was observed in association with lymphocyte profiles. In the hypopigmented areas the melanocytes showed slight regressive changes. An interesting finding is the apparent increase of the melanocyte surface directly faced with the basal lamina. No structural alterations were detected in the dermis except occasional lymphocyte perivascular infiltrates. A rich nervous network made mainly of unmyelinated axons was observed in the papillary dermis (Fig. 3). Nerve fibres did not show structural abnormalities and were regularly surrounded by normally-looking Schwann cells.
V. Cavallari
et al. /Journal
of Dermatological
Science 13 (1996) 87-92
Fig. I. Basal keratinocytes. The number of melanosome profiles is reduced. An unmyelinated mal junction (uranyl acetate and lead citrate, x 15 000).
89
nerve bundle lies at the dermo-epider-
90
V. Cavallari
et al. /Journal
of’Dermatologica1
Science 13 (1996) 87-92
Fig. 2. Regressive changes of melanocytes and keratinocytes. A melanocyte profile with increase of cytoplasmic organelles and ninent vacuolization is associated with keratinocyte profiles containing melanosome aggregates. A neighboring keratinc xyte ibot tom right) is devoid of melanosomes ( x 8000). Inset: a detail of an intercellular contact showing the complete segregatic m of mosomes in the cytoplasm of a keratinocyte ( x 20000).
V. Cavallari
et al. 1 Journal of Dermatological
Science 13 (1996) 87-92
91
Fig. 3. (a) Nerve fibers in the dermis. An unmyelinated axon in close relationship with the basal keratinocytes ( x 10000). (b) A melanocyte apparently protruding in the dermis ( x 12000).
92
V. Caoallari et al. I Journal
of Drrmatological
4. Discussion
A functional abnormality of melanocytes is generally accepted in HI. A disorder of the melanocyte metabolism involving the selective suppression of the eumelanin synthesis was recently demonstrated in HI IS]. In the two cases reported here the differential diagnosis was made against the other linear and whorled pigmentations, i.e. nevus depigmentosus, incontinentia pigmenti, linear and whorled nevoid hypermelanosis [6,7]. The morphological findings confirm the previously reported observations [S- lo]. In particular, the apparent correlation of the hypopigmentation with a local loss of functioning melanocytes is confirmed in our observations. Normally pigmented keratinocytes can be detected in relation with preserved melanocytes, whereas in the hypopigmented zones no melanocytes were found. In agreement with other ultrastructural observations [3], an apparent increase in nerve endings was observed in the two new casesdescribed here. These peripheral nervous structures did not show pathological changes. The role of the dermal nerve fibres in the regulation of the pigmentation was not sufficiently explored. It is conceivable that neurotransmitters could act on the phenotypic expression of the various cells lying in the dermoepidermal microenvironment. An increased melanogenesis can be a non-specific consequence of a pathologic process involving the production of inflammatory release factors proved to stimulate the nerve endings. On the other hand, hypopigmentation can be observed in denervated cutaneous areas in association with other hypotrophic changes of the skin and annexes. Therefore, we could suggest that Ito’s linear and whorled hypopigmentation is an inhibitory signal carried by the nerve endings. The regressive changes of melanocytes associated with similar changes of the neighbouring keratinocytes were found only in one case. This could reflect an early stage in the pathogenesis of the hypopigmented lesions, whereas in the majority of fields the melanocyte profiles are simply absent.
Science 13 (1996) 87-92
The frequent appearance of the melanocytes in close relationship with the basal lamina, and, occasionally, the apparent protrusion of parts of cytoplasm towards the dermis is difficult to explain. This arrangement is infrequent in normal skin biopsies, where the melanocyte profiles are regularly spaced. However, in conditions involving a functional activation and/or a numerical increase of melanocytes, the probability of finding contacts with the basal lamina is increased. In our experience, melanocyte profiles are seen prevalently surrounded by keratinocytes. Contacts with the basal lamina involve only a limited amount of the cell surface. Regressive changes of melanocytes, a reduction of the cytoplasmic processes and a tendency towards a circular contour could account in part for their basal location.
References [I] Castroviejo IP, Lopez-Rodriguez L, Medina MC, Salamanta-Maesso C, Roche-Herrero C. Hypomelanosis of Ito. Neurological complications in 34 cases.Can J Neurol Sci 15: 124-129, 1988. [2] Ruiz-Maldonado R, Toussaint S, Tamayo L, Laterza A, del Castillo V. Hypomelanosis of Ito: diagnostic criteria and report of 41 cases. Pediatr Dermatol 9: I-IO, 1992. [3] Morohashi M, Hashimoto K, Goodman TF, Newton DE, Rist T. Ultrastructural studies of vitiligo, Vogt-Koyanagi syndrome, and incontinentia pigmenti achromians. Arch Dermatol 113: 7555766, 1977. [4] Schepis C, Cavallari V, Elia M, Ussia AF, Pontieri F. Hypomelanosis of Ito: ultrastructural study. Eur J Pediatr Dermatol 2: 115-120, 1992. [S] Fukai K, Ishii M, Wakamatsu K, lto S, Sakamoto H, Fujiwara H, Ohno A, Hamada T. Selective decrease of eumelanin in hypopigmented epidermis of hypomelanosis of Ito. Pediatr Dermatol I I: 261-263, 1994. [6] Harre J, Millikan LE. Linear and whorled pigmentation. Int J Dermatol 33: 529-537, 1994. [7] Schepis C. Congenital or perinatal macules distributed according the Blaschko’s lines. Eur J Pediatr Dermatol 4: 73-75,
1994.
Grosshans EM, Stoebner P, Bergoend H, Stall C. Incontinentia pigmenti achromians (ITO). Etude clinique et histo-pathologique. Dermatologica 1971; 142: 65-78 [9] Nordlund JJ, Klaus SN, Gino J. Hypomelanosis of Ito. Acta Dermatovener (Stockholm) 57: 261-264, 1977; [IO] Cambazard F, Hermier C, Thivolet J, Perrot H. Hypomelanose de Ito. Revue de la litterature a propos de 3 cas. Ann Dermatol Venereol 113: 15-23, 1986. [8]