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Morton's neuroma: an immunohistochemical study
The Foot ( 1996) 6.63-65 0 1996 Pearson Professmnal Ltd
Morton’s neuroma: an immunohistochemical
study
U. E. Pazzaglia,S. Moalli, M. Leutner, R. Gera Clinica Ovtopedica, Facolta’ di Medicina e Chirurgia, Universita’ di Pavia, Varese, Italy SUMMARY. Fifteen swellings of the interdigital nerve of 12 patients with Morton’s metatarsalgia and 3 controls were studied by routine histology and immunohistochemical technique employing monoclonal antibodies against neurofilaments, human epithelial membrane antigen and a polyclonal antibody anti S-100 for the myelinic sheath. With the latter methods, individual nerve fasciculi were accurately identified in the context of the connective tissue mass of the ‘neuroma’. The basic aspect of the lesion showed by this study is the proliferation of connective cells affecting not only the perineurium and the endoneurium, but also individual nerve fasciculi. The latter were classified as compact or loose in relation to the fibrous proliferative process taking place inside fasciculi. Comparison of Morton’s ‘neuroma’ and controls showed a prevalence of loosened fasciculi in the former. Fibroblastic proliferation and dissociation of the nerve fibres involved individual nerves in different degrees; no correlation was observed between pathological features and duration of symptoms. In more than two-thirds of cases in this series, Morton’s metatarsalgia was associated with cavus or forefoot deformities.
INTRODUCTION
women and 2 men; in 1 case, pain was present in both feet and 2 neuromata were found in the right and left foot respectively. Another patient had 2 neuromata in the same foot. In total, 15 specimens were studied, 11 from the third intermetatarsal space and 4 from the fourth. The patients were aged between 23 and 75 years (mean 55 years). The duration of symptoms varied from 2 to 36 months (mean 4 years). The shape of the foot was normal in 3 patients, cavus in 5 and with various deformities of the forefoot in 4. In none of these cases were local infiltrations performed before surgery. Control specimens were obtained from 3 interdigital nerves taken by routine autopsy of patients whose clinical history was negative for Morton’s metatarsalgia. The specimens were fixed in phosphate buffered formalin and embedded in paraffin. Five micron thick sections were routinely stained with haematoxylin-eosin. Immunohistochemical investigation was performed using the avidin-byotin-peroxidase complexlo using the following antisera:
A variety of histopathological changes involving nerves, vessels and surrounding connective tissue has been reported in the knob-like swelling at the bifurcation of the interdigital nerve known as Morton’s neuroma.1-5 Nevertheless, the pathogenesis remains uncertain as it has been impossible to differentiate primary and secondary histopathological lesions. Also, intrastructural studies did not answer these questions.‘a3 There is a general agreement about the mechanical origin of the disease, but the pathogenesis is debated: nerve lesions and fibrosis have been suggested to be secondary to vessel damage and ischaemia,6x7 while others postulate a primary degenerative lesion of nerve fibres.4.8 In this study immuno histochemical methods have been employed and they allowed a better identification of neural structures in the ‘neuroma’.
MATERIALS
AND METHODS
The ‘neuromata’ of the interdigital nerve of 12 patients who presented with Morton’s metatarsalgia were resected using a plantar incision. There were 10
1. A monoclonal antibody to neurofilaments (dilution l/200, SANBIO); 2. A monoclonal antibody to human epithelial membrane antigen (dilution l/200, DAKO); 3. A polyclonal antibody anti-S100 (dilution l/400, DAKO) .
Correspondence to Professor Ugo E. Pazzaglia MD, Clinica Ortopedica, 2a Facolta’ di Medicina e Chirurgla dell’Universita’ Pavia. Ospedale F. Del Ponte, 21100 Varese, Italy Fax: +332-288956.
Normal human sympathetic paraganglia were used as positive controls. Specificity controls were performed according to Polak & Van Noorden.”
di
63
64 The Foot
Fig. 1-Monoclonal antibody against neurofilaments (250x). Example of a compact nervous fasciculum; nerve fibres are closely packed together and are surrounded by endonervium.
Since nervous fasciculi were scattered in an abundant mass of connective tissue, without the structured organization of peripheral nerves, a strictly quantitative evaluation of nerve bundles is questionable; a semiquantitative approach according to the following criteria was followed. The number of fasciculi in each histological slide was evaluated, and fasciculi were assigned to two classes: compact, when nervous fibres were densely packed inside endonervium (Fig. 1); or loose, when connective tissue was present between fibres (Fig. 2). Compact and loose fasciculi, evaluated on blinded slides, were expressed as a percentage of the total number of fasciculi.
Fig. SMonoclonal antibody against neurofilaments (250x). Example of a loosened nervous fasciculum; proliferation of connective cells between nerve fibres; endonervium is not clearly marked.
RESULTS The control interdigital nerves had the appearance of a thin band, while all cases of Morton’s metatarsalgia presented with a knob-like swelling at the bifurcation of the interdigital nerve (Morton’s neuroma). At microscopical examination (Fig, 3A), sections of the former stained with monoclonal antibodies to neurofilaments showed well defined fasciculi with neural fibres closely packed (Fig. 3B); fasciculi were encapsulated by flattened cells stained by HEMA antibody (Fig. 3C); Swann’s cells in close contact with neurofilaments, were stained by polyclonal antibody SlOO. Among fasciculi, a loose connective tissue with arterioles, capillaries and venules was present. Other fasciculi were less compact, due to the presence of connective cells among neurofilaments. The Morton’s neuroma was formed by a connective tissue nodule and neural fasciculi were scattered in this mass formed by interwoven, collagenous, fibrous tissue vessels and deposits of amorphous material (Fig. 4). Nervous fasciculi were identified by the antibody against neurofilaments; both the compact and loose features were represented. The relative distribution of compact and loose fasciculi is reported in Table 1. No correlation between duration of symptoms and histopathological findings was present in this series of Morton’s neuroma cases.
Fig. 3-(A) Haematoxylin-eosin (400x). Neural fascrculum as shown by routine histology; neural fibres cannot be identified. (B) Monoclonal antibody against neurofilaments (400x). Neural fibres are well shown by immunostaining. (C) Monoclonal antibody against human epitelial membrane antigen (400x). The epmeural sheath is clearly identified by the immunostaining.
Morton’s neuroma
Fig. 4-Monoclonal Amorphous material observed in Morton’s
antibody against neurofilaments (250x). deposition inside nervous fascicuh was often neuroma.
Table 1 Semiquantitative evaluation of compact fasciculi in Morton’s neuroma and in controls
65
Whether the latter is a primary lesion or secondary to vascular changes remains a matter of speculation, as both are present in the earlier stages, according to the classification of Lassman & Machacek.15 A more detailed description of the evolutive phases of the disease based on correlation between histopathological changes and clinical signs (for example the duration of symptoms) was not possible. The progressive fibrosis may result from repeated trauma of the nerve in the interdigital cleft3Jh In more than two-thirds of cases in this series, Morton’s disease appeared in feet with cavus or forefoot deformity and this further supports a mechanical pathogenetic mechanism.
and loose REFERENCES
Morton’s (n = 15) Controls
Fasciculi (mean for slide)
Type compact
‘Me loose
15.2 22.5
8.8% 32.2%
91.2% 67.8%
neuroma (n = 3)
DISCUSSION
The polymorphous pathology of Morton’s disease prompted different pathogenetic theories. Either the vascular changes and ischaemia,*a6 inflammation, 12~13 nervous proliferation (neuromata)4,‘4 or proliferation of perineural cells2 have been suggested as the primary lesion. Electron microscopy studies have given evidence that the lesion consists of a progressive fibrosis which envelopes and disrupts nerves and arteries. However, no evidence of nerve fibre proliferation or a specific inflammatory process was found.2,3 The immuno histochemical technique employed in this study allowed recognition of individual nerve fasciculi in the neuroma and confirmed the view that the basic aspect of the lesion is proliferation of connective cells also affecting individual nerve fasciculi. In the present study, no attempt was made to compare the number of nerve fibres and the ratio of myelinated-unmyelinated fibres between Morton’s ‘neuromata’ and controls. Even with the limits of semiquantitative evaluation of compact and loose fasciculi, a clear prevalence of the latter, involved by the connective proliferation process was evident in Morton’s ‘neuromata’. The fibroblastic proliferation and the dissociation of the nerve fasciculi and bundles was the most striking feature of the disease, with a different degree of involvement of individual fasciculi.
1. Guiloff R J, Scadding J W. Kleneman L. Morton’s metatarsalgra. Clinical, electrophysiological and histologtcai observations. J Bone Joint Surg 1984.66B: 586-591 2. Ha’Eri G B, Fornasier V L, Schatzkerr J. Morton’s Neuroma ~ pathogenesis and ultrastructure. Clin Orthop 1979; 141: 256-259. 3. Lassmann G. Morton’s Toe. Clinical, light and electron microscopic investigations in 133 cases. Chn Orthop 1979: 142: 73-84. 4. McElvenny R T. Etiology and surgtcal treatment of intractable pain about the fourth metatarso-phalangeal joint. J Bone Joint Surg 1943; 25: 6755679. Volpe A, Volpato P. La sindrome di Thomas G. Morton. Chir de1 Piede 1987; 11: 213-218. Nissen K I. Plantar digital neuritis (Morton’s metatarsalgla). J Bone Joint Surg 1984,30B: 8494. Ringertz N, Unander-Scharin L. Morton’s disease: a clinical and pathoanatomical study. Acta Orthop Stand 1950; 19: 327-348. 8. Meachim C, Abberton M J. Histological findings in Morton’s metatarsalgia. J Path01 1971: 103: 209-217. 9. Carson J H, Martin J H, Lyn J A. Formahn fixation for electron microscopy: a revaluation. Am J Clin Path01 1973: 59: 365-373. 10. Hsu S M, Rame L, Fanger H. Use of avidin-biotin-peroxidase complex (ABC) in immunoaeroxidase techniaue. J Histochem Cytochem 1981; 29: 577-580. 11. Polak J M. Van Noorden S. Immunocytochemistry. Modern methods and applications, 2nd ed. Bristol, 1986. 12. Bossley C J> Carney P C. The intermetatarso-phalangeal bursa. Its significance m Morton’s metatarsalgra. J Bone Joint Surg 1980; 62B: 184-187. 13. Reed R J, Bliss B 0. Morton’s neuroma, regressive and productive intermetatarsal elastofibrosis. Arch Path01 1971: 95: 1233129. 14. Ochoa J. The primary nerve fibre pathology of plantar neuromas: a model of chronic entrapment. J Neuropathol Exp Nemo1 1976; 35: 370-378. 15. Lassmann G, Machacek J. Clinical features and histology of Morton’s metatarsalgia. Wien Klin Wochenschr 1969; 81: 55-58. 16. Volpe A, Melanotte PL, Torresin P. Rugge M Le sindroml canalicolari de1 piede. Eziopatogenesr ed anatomia patologica. Chir de1 Piede 1989; 13: S-15.
Morton’s neuroma: an immunohistochemical
study
U. E. Pazzaglia,S. Moalli, M. Leutner, R. Gera Clinica Ovtopedica, Facolta’ di Medicina e Chirurgia, Universita’ di Pavia, Varese, Italy SUMMARY. Fifteen swellings of the interdigital nerve of 12 patients with Morton’s metatarsalgia and 3 controls were studied by routine histology and immunohistochemical technique employing monoclonal antibodies against neurofilaments, human epithelial membrane antigen and a polyclonal antibody anti S-100 for the myelinic sheath. With the latter methods, individual nerve fasciculi were accurately identified in the context of the connective tissue mass of the ‘neuroma’. The basic aspect of the lesion showed by this study is the proliferation of connective cells affecting not only the perineurium and the endoneurium, but also individual nerve fasciculi. The latter were classified as compact or loose in relation to the fibrous proliferative process taking place inside fasciculi. Comparison of Morton’s ‘neuroma’ and controls showed a prevalence of loosened fasciculi in the former. Fibroblastic proliferation and dissociation of the nerve fibres involved individual nerves in different degrees; no correlation was observed between pathological features and duration of symptoms. In more than two-thirds of cases in this series, Morton’s metatarsalgia was associated with cavus or forefoot deformities.
INTRODUCTION
women and 2 men; in 1 case, pain was present in both feet and 2 neuromata were found in the right and left foot respectively. Another patient had 2 neuromata in the same foot. In total, 15 specimens were studied, 11 from the third intermetatarsal space and 4 from the fourth. The patients were aged between 23 and 75 years (mean 55 years). The duration of symptoms varied from 2 to 36 months (mean 4 years). The shape of the foot was normal in 3 patients, cavus in 5 and with various deformities of the forefoot in 4. In none of these cases were local infiltrations performed before surgery. Control specimens were obtained from 3 interdigital nerves taken by routine autopsy of patients whose clinical history was negative for Morton’s metatarsalgia. The specimens were fixed in phosphate buffered formalin and embedded in paraffin. Five micron thick sections were routinely stained with haematoxylin-eosin. Immunohistochemical investigation was performed using the avidin-byotin-peroxidase complexlo using the following antisera:
A variety of histopathological changes involving nerves, vessels and surrounding connective tissue has been reported in the knob-like swelling at the bifurcation of the interdigital nerve known as Morton’s neuroma.1-5 Nevertheless, the pathogenesis remains uncertain as it has been impossible to differentiate primary and secondary histopathological lesions. Also, intrastructural studies did not answer these questions.‘a3 There is a general agreement about the mechanical origin of the disease, but the pathogenesis is debated: nerve lesions and fibrosis have been suggested to be secondary to vessel damage and ischaemia,6x7 while others postulate a primary degenerative lesion of nerve fibres.4.8 In this study immuno histochemical methods have been employed and they allowed a better identification of neural structures in the ‘neuroma’.
MATERIALS
AND METHODS
The ‘neuromata’ of the interdigital nerve of 12 patients who presented with Morton’s metatarsalgia were resected using a plantar incision. There were 10
1. A monoclonal antibody to neurofilaments (dilution l/200, SANBIO); 2. A monoclonal antibody to human epithelial membrane antigen (dilution l/200, DAKO); 3. A polyclonal antibody anti-S100 (dilution l/400, DAKO) .
Correspondence to Professor Ugo E. Pazzaglia MD, Clinica Ortopedica, 2a Facolta’ di Medicina e Chirurgla dell’Universita’ Pavia. Ospedale F. Del Ponte, 21100 Varese, Italy Fax: +332-288956.
Normal human sympathetic paraganglia were used as positive controls. Specificity controls were performed according to Polak & Van Noorden.”
di
63
64 The Foot
Fig. 1-Monoclonal antibody against neurofilaments (250x). Example of a compact nervous fasciculum; nerve fibres are closely packed together and are surrounded by endonervium.
Since nervous fasciculi were scattered in an abundant mass of connective tissue, without the structured organization of peripheral nerves, a strictly quantitative evaluation of nerve bundles is questionable; a semiquantitative approach according to the following criteria was followed. The number of fasciculi in each histological slide was evaluated, and fasciculi were assigned to two classes: compact, when nervous fibres were densely packed inside endonervium (Fig. 1); or loose, when connective tissue was present between fibres (Fig. 2). Compact and loose fasciculi, evaluated on blinded slides, were expressed as a percentage of the total number of fasciculi.
Fig. SMonoclonal antibody against neurofilaments (250x). Example of a loosened nervous fasciculum; proliferation of connective cells between nerve fibres; endonervium is not clearly marked.
RESULTS The control interdigital nerves had the appearance of a thin band, while all cases of Morton’s metatarsalgia presented with a knob-like swelling at the bifurcation of the interdigital nerve (Morton’s neuroma). At microscopical examination (Fig, 3A), sections of the former stained with monoclonal antibodies to neurofilaments showed well defined fasciculi with neural fibres closely packed (Fig. 3B); fasciculi were encapsulated by flattened cells stained by HEMA antibody (Fig. 3C); Swann’s cells in close contact with neurofilaments, were stained by polyclonal antibody SlOO. Among fasciculi, a loose connective tissue with arterioles, capillaries and venules was present. Other fasciculi were less compact, due to the presence of connective cells among neurofilaments. The Morton’s neuroma was formed by a connective tissue nodule and neural fasciculi were scattered in this mass formed by interwoven, collagenous, fibrous tissue vessels and deposits of amorphous material (Fig. 4). Nervous fasciculi were identified by the antibody against neurofilaments; both the compact and loose features were represented. The relative distribution of compact and loose fasciculi is reported in Table 1. No correlation between duration of symptoms and histopathological findings was present in this series of Morton’s neuroma cases.
Fig. 3-(A) Haematoxylin-eosin (400x). Neural fascrculum as shown by routine histology; neural fibres cannot be identified. (B) Monoclonal antibody against neurofilaments (400x). Neural fibres are well shown by immunostaining. (C) Monoclonal antibody against human epitelial membrane antigen (400x). The epmeural sheath is clearly identified by the immunostaining.
Morton’s neuroma
Fig. 4-Monoclonal Amorphous material observed in Morton’s
antibody against neurofilaments (250x). deposition inside nervous fascicuh was often neuroma.
Table 1 Semiquantitative evaluation of compact fasciculi in Morton’s neuroma and in controls
65
Whether the latter is a primary lesion or secondary to vascular changes remains a matter of speculation, as both are present in the earlier stages, according to the classification of Lassman & Machacek.15 A more detailed description of the evolutive phases of the disease based on correlation between histopathological changes and clinical signs (for example the duration of symptoms) was not possible. The progressive fibrosis may result from repeated trauma of the nerve in the interdigital cleft3Jh In more than two-thirds of cases in this series, Morton’s disease appeared in feet with cavus or forefoot deformity and this further supports a mechanical pathogenetic mechanism.
and loose REFERENCES
Morton’s (n = 15) Controls
Fasciculi (mean for slide)
Type compact
‘Me loose
15.2 22.5
8.8% 32.2%
91.2% 67.8%
neuroma (n = 3)
DISCUSSION
The polymorphous pathology of Morton’s disease prompted different pathogenetic theories. Either the vascular changes and ischaemia,*a6 inflammation, 12~13 nervous proliferation (neuromata)4,‘4 or proliferation of perineural cells2 have been suggested as the primary lesion. Electron microscopy studies have given evidence that the lesion consists of a progressive fibrosis which envelopes and disrupts nerves and arteries. However, no evidence of nerve fibre proliferation or a specific inflammatory process was found.2,3 The immuno histochemical technique employed in this study allowed recognition of individual nerve fasciculi in the neuroma and confirmed the view that the basic aspect of the lesion is proliferation of connective cells also affecting individual nerve fasciculi. In the present study, no attempt was made to compare the number of nerve fibres and the ratio of myelinated-unmyelinated fibres between Morton’s ‘neuromata’ and controls. Even with the limits of semiquantitative evaluation of compact and loose fasciculi, a clear prevalence of the latter, involved by the connective proliferation process was evident in Morton’s ‘neuromata’. The fibroblastic proliferation and the dissociation of the nerve fasciculi and bundles was the most striking feature of the disease, with a different degree of involvement of individual fasciculi.
1. Guiloff R J, Scadding J W. Kleneman L. Morton’s metatarsalgra. Clinical, electrophysiological and histologtcai observations. J Bone Joint Surg 1984.66B: 586-591 2. Ha’Eri G B, Fornasier V L, Schatzkerr J. Morton’s Neuroma ~ pathogenesis and ultrastructure. Clin Orthop 1979; 141: 256-259. 3. Lassmann G. Morton’s Toe. Clinical, light and electron microscopic investigations in 133 cases. Chn Orthop 1979: 142: 73-84. 4. McElvenny R T. Etiology and surgtcal treatment of intractable pain about the fourth metatarso-phalangeal joint. J Bone Joint Surg 1943; 25: 6755679. Volpe A, Volpato P. La sindrome di Thomas G. Morton. Chir de1 Piede 1987; 11: 213-218. Nissen K I. Plantar digital neuritis (Morton’s metatarsalgla). J Bone Joint Surg 1984,30B: 8494. Ringertz N, Unander-Scharin L. Morton’s disease: a clinical and pathoanatomical study. Acta Orthop Stand 1950; 19: 327-348. 8. Meachim C, Abberton M J. Histological findings in Morton’s metatarsalgia. J Path01 1971: 103: 209-217. 9. Carson J H, Martin J H, Lyn J A. Formahn fixation for electron microscopy: a revaluation. Am J Clin Path01 1973: 59: 365-373. 10. Hsu S M, Rame L, Fanger H. Use of avidin-biotin-peroxidase complex (ABC) in immunoaeroxidase techniaue. J Histochem Cytochem 1981; 29: 577-580. 11. Polak J M. Van Noorden S. Immunocytochemistry. Modern methods and applications, 2nd ed. Bristol, 1986. 12. Bossley C J> Carney P C. The intermetatarso-phalangeal bursa. Its significance m Morton’s metatarsalgra. J Bone Joint Surg 1980; 62B: 184-187. 13. Reed R J, Bliss B 0. Morton’s neuroma, regressive and productive intermetatarsal elastofibrosis. Arch Path01 1971: 95: 1233129. 14. Ochoa J. The primary nerve fibre pathology of plantar neuromas: a model of chronic entrapment. J Neuropathol Exp Nemo1 1976; 35: 370-378. 15. Lassmann G, Machacek J. Clinical features and histology of Morton’s metatarsalgia. Wien Klin Wochenschr 1969; 81: 55-58. 16. Volpe A, Melanotte PL, Torresin P. Rugge M Le sindroml canalicolari de1 piede. Eziopatogenesr ed anatomia patologica. Chir de1 Piede 1989; 13: S-15.