► [Broad or dense clavicles]
The clavicles are involved to a variable extent in the majority of the inherited disorders with generalized hyperostosis and sclerosis, defective bone modeling, or both. Clavicular broadening and thickening in such cases are usually bilateral and symmetrical, reflecting a systemic disorder. Yet the distribution of the defect within the clavicle does vary among different disorders. As a result, the clavicle can have a homogeneously broad and/or dense appearance or show involvement of individual portions (medial, central, or lateral). For example, in oculo-dento-os-seous dysplasia (OMIM 257850, 164200), a disorder with 'increased bone density and metaphyseal involvement' (International Nomenclature and Classification of the Osteochondrodysplasias 1997), the clavicles show a significant expansion of their medial portions, while the ribs are only slightly enlarged. Similarly, widening of the medial half of the clavicle is observed in endosteal hyperostosis (van Buchem, OMIM 239100), a disorder with 'increased bone density and diaphyseal involvement.' Although only rarely, involvement of the medial two-thirds of the clavicles is seen in diaphyseal dysplasia (Camurati-Engelmann, OMIM 131300). On the other hand,ho-mogeneous clavicular involvement occurs in several other sclerosing bone dysplasias, including dysos-teosclerosis, Pyle dysplasia (Fig. 2.35), craniodiaphy-seal dysplasia, and Lenz-Majewski syndrome. Lenz-Majewski syndrome (OMIM 151050), a rare disorder of unknown origin (all cases have been sporadic, but new mutation for a dominant gene has been suggested), is characterized by widespread sclerosis of the calvarium, skull base, and vertebrae; uniformly broad and thick clavicles and ribs; proximal sympha-langism; short or absent middle phalanges; osteo-penic, radiolucent metaphyses and epiphyses; retarded skeletal maturation; characteristic facies (large head, prominent scalp veins, large and floppy ears, hypertelorism); loose skin; and mental retardation (Lenz and Majewski 1974; Borlin and Whitley 1983). Homogeneous expansion and sclerosis of the clavicles are also features in the rare autosomal dominant distal osteosclerosis (OMIM 126250), a clinically silent disorder characterized by mild calvarial and skull base sclerosis, bowing and hyperostosis of the long bones in the forearms and shanks, sclerotic striae in the pelvis and femurs, and localized sclerosis of the vertebral pedicles (Beighton et al. 1980).
Several other inherited conditions are associated with widening and/or sclerosis of the clavicles. Fryns syndrome (OMIM 229850) is an autosomal recessive condition characterized by diaphragmatic abnormalities (89%), coarse facies (100%), macrostomia (92%), and distal digital hypoplasia (short terminal phalanges and hypoplastic nails) (100%) (Jones 1997). The majority of affected individuals are stillborn or die soon after birth. A broad appearance of the medial ends of the clavicles is observed. Cranio-facial features include a coarse face, misshapen ears, cleft lip/palate, micrognathia, broad nasal bridge, and anteverted nares. Genitourinary and anal anomalies, central nervous system malformations, cardiac defects, omphalocele, and Hirschsprung 'disease' are additional features (Bamforth et al. 1989). In Holt-Oram syndrome (OMIM 142900) there is a wide range of severity of defects in the upper limb and shoulder girdle. The clavicles can be either normal or hypoplastic,with thick outer portions that may eventually articulate with the coracoid process. In trisomy 8 mosaicism syndrome, in addition to the rib gap anomaly (Kozlowski et al. 1988), emphasis has been put on other skeletal anomalies involving the chest, including the symmetrical widening of the clavicles with slight 'handlebar' configuration, widened ribs, and vertically elongated, narrow thorax (Fig. 2.36) (Beighton et al. 1999). The presence of these chest abnormalities in a mentally retarded patient should raise the suspicion of trisomy 8 mosaicism (Beighton et al. 1999). Thick, broad and short clavicles have recently been reported in chromosome 21 partial monosomy syndrome, a rare disorder resulting either from distal 21q deletion or ring chromosome formation (Fig. 2.37). The clinical manifestations vary from mild to severe and can be considered the counterparts of those occurring in Down syndrome, including hypertonia, prominent occiput, large ears, broad nose, and down-slanted palpebral fissures (Wang and Aftimos 1999). Occipital horn syndrome (cutis laxa X-linked, OMIM 304150), formerly designated Ehlers-Danlos syndrome type IX, is an X-linked re-cessively inherited condition caused by abnormalities in copper metabolism. The genetic defect is allelic to Menkes syndrome. Radiologic manifestations include bilateral and symmetrical occipital horns; broad, hammer-shaped clavicles; carpal fusion; widening and bowing of the radius, ulna, and humerus; narrow thorax; undercalcified long bones; and coxa valga. Distinctive clinical features common to all patients with this syndrome are a characteristic facies (narrow face, high forehead), soft and lax skin, coarse hair, hypermobility of finger joints, limitation
Fig. 2.35. Pyle disease in a woman patient. There is marked widening of the clavicles and ribs
Fig. 2.35. Pyle disease in a woman patient. There is marked widening of the clavicles and ribs
Fig. 2.37. Partial monosomy 21 syndrome in a male newborn delivered at 37 weeks of gestation. Note thick, broad clavicles on both sides.Although not mentioned by the original authors, discontinuity of both clavicles at their midportion (congenital pseudarthrosis) is likely. (From Wang and Aftimos 1999)
of motion at the elbows, chronic diarrhea, and genitourinary abnormalities (Tsukahara et al. 1994). The triad of occipital horns, short and broad clavicles, and bladder diverticula is considered characteristic of this condition (Sartoris et al. 1984). Both vein varices and arterial aneurysms, the latter typically associated with Ehlers-Danlos syndrome types I and IV, can occur in the occipital horn syndrome (Mentzel et al. 1999).
A wide variety of acquired conditions (infections, trauma, malignancies, chronic granulomatous diseases, inflammatory diseases) may also cause clavicular thickening and sclerosis, either focal or diffuse, usually by inducing a periosteal reaction with new bone deposition in the periosteum and/or neighboring soft tissues. A discussion of these disorders is be yond the scope of this book. Nevertheless, a group of unique disorders involving the bone and skin, intermediate between an infectious and an inflammatory process of unknown cause, deserves mention, because of the preferential localization of these disorders to the anterior chest wall (medial ends of the clavicles, sternum, and upper ribs). These disorders are regarded as sharing clinical, radiologic, and pathophysiologic characteristics and are subsumed under the designation SAPHO syndrome, an acronym for synovitis, acne, pustulosis, hyperostosis, and osteitis (Chamot et al. 1987). The following disease entities have been included under the label of SAPHO: chronic recurrent multifocal osteomyelitis; sterno-costo-clavicular hyperostosis; and pustulotic arthro-osteitis. The fact that pustulotic arthro-os-
Fig. 2.38 a-c. Chronic recurrent multifocal osteomyelitis (CRMO) in a girl. a At her first examination she was 6 years and 6 months of age. There is lytic destruction (open arrow) of the sternal end of the left clavicle, associated with slight periosteal new bone formation. The right clavicle is normal. b A tomogram obtained 5 months later shows lytic destruction (open arrows) in the medial part of both clavicles and periosteal new bone formation (arrowhead). c At an examination 9 months later, foci of lytic destruction are still evident on both sides (open arrows). Periosteal new bone formation, hyperostosis, and sclerosis are dominant features on the right side. (From Jurik and Moller 1986)
teitis is a nonspecific designation loosely used to describe musculoskeletal manifestations associated with pustulosis palmaris and plantaris underscores the difficulties inherent in a proper categorization of these disorders. Resnick and Niwayama (1995) provided an extensive discussion on the pathophysiolo-gy of these syndromes and the appropriateness of the designation SAPHO. Certainly it has the advantage of emphasizing the fundamental cutaneous and osseous lesions of these disorders. For instance, the term 'hyperostosis' accurately describes the bone manifestations, dominated as they are by trabecular and cortical thickening, narrowing of the medullary canal, and irregularities of the external bone surface. Chronic recurrent multifocal osteomyelitis (CRMO) is a disorder of unknown etiology, affecting children and adolescents, with preferential involvement of the medial ends of the clavicles and metaphyses of the long bones, especially in the lower extremities. Less frequently, other osseous structures, such as the vertebrae, ribs, pelvis, and small bones in the hands and feet, are altered. The lesions have a striking degree of symmetrical distribution. Permeative bone destruction and subsequent bone sclerosis are the dominant pathological changes. At the level of the clavicles, massive enlargement of the sternal ends is common (Fig. 2.38 a-c). Histology usually reveals plasma cell infiltration. No causative organisms can be consistently detected (Jurik et al. 1985; Jurik and Moller 1986). Initial clinical symptoms include pain,tender ness, and swelling, and the further clinical course is one of alternating exacerbations and remissions. Pustular lesions of the palms and soles (pustulosis palmaris et plantaris) identical to those encountered in sternocostoclavicular hyperostosis (see subsequent discussion) may be found, suggesting a link between the two conditions as well as one between anterior chest wall lesions and the skin lesions themselves. Incidentally, psoriasis can also produce both skin lesions of the same type as described above and osseous lesions in the sternoclavicular area. Imprecise use of terminology has led to confusion with other distinct disorders, notably condensing osteitis of the clavicle, a noninflammatory disorder confined to the clavicle and affecting mainly adult females (Appell et al. 1983). Sternocostoclavicular hyperosto-sis is a separate hyperostotic syndrome sharing similarities with Paget disease and characterized by painful, condensing hypertrophy of the sternum, both clavicles, and the upper ribs. Middle-aged individuals and elderly, especially men, are most commonly affected. Clinically, the disease produces swelling of the upper chest area and pulling pain in the sternum, clavicles, upper ribs and shoulders, exacerbated by cold and humidity. Pustulosis palmaris et plantaris are commonly associated findings. Radiographs usually show bilateral, symmetrical enlargement and thickening of the clavicles,sternoclavicular synostosis, hyperostosis of the sternum and upper ribs, and varying degrees of involvement of the
Fig. 2.40. Condensing osteitis of the clavicle in a 37-year-old man with chronic medial left clavicular pain accentuated by abduction of the arm. Note sclerosis of the medial end of the clavicle (arrow) and a normal joint space. (From Noonan et al. 1998)
sacroiliac joints (Fig. 2.39). Increased uptake on skeletal scintigraphy and hyperostotic sclerosis of the cancellous bone on biopsy specimens are characteristic (Kohler et al. 1977; Goossens et al. 1985). Another sclerosing disorder affecting the medial end of the clavicle, without associated cutaneous lesions and therefore unrelated to the SAPHO syndrome, is condensing osteitis of the clavicle (Greenspan et al. 1991). This is a benign, self-limiting condition of unknown cause, showing a predilection for unilateral involvement of the medial end of the clavicle and most typically affecting women of childbearing age, so that it could possibly be related to osteitis con-densans ilii and osteitis pubis. Reports of affected men have also been published (Noonan et al. 1998) (Fig. 2.40). A history of stress or strain on the sternoclavicular joint (related to sport or occupational activities) is common. Pain and swelling over the medial end of the clavicle are frequent presenting symp toms. The pathological changes consist in thickening of trabeculae with eburnation of the cancellous bone and periosteal reaction. Plasma cell infiltrate has been reported within foci of sclerotic bone, suggesting a link with chronic recurrent multifocal osteomyelitis (CRMO) and POEMS (polyneuropathy, organomegaly, endocrinopathy, M protein dyscrasia, skin changes) syndrome, a plasma cell dyscrasia with skin lesions and sclerosis of bones (Resnick and Niwayama 1995). The sternoclavicular joint is not affected. Radiographs reveal bone sclerosis and mild enlargement of the sternal end of the clavicle, often associated with osteophyte formation. The differential diagnosis against ischemic necrosis of the medial segment of the clavicle (Friedrich's disease) may be difficult, although the different age distribution (children and adolescents most commonly affected by is-chemic necrosis) and the presence of a small defect of the articular surface in Friedrich's disease should allow differentiation between the two entities (Greenspan et al. 1991).
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