CASE SUMMARY:

A 47-year-old male presented with a history of left foot pain, discomfort, difficulty standing and walking, and a sensation of "walking on marbles" for several months; he also was unable to fit his foot into his shoe. The patient's past medical history was significant for left foot sesamoiditis and remote surgical procedures on the left foot. A plain radiograph of the left foot showed mixed sclerosing dystrophy in addition to a "candle-wax-like" appearance and thickening of the cortices of the calcaneum, third through fifth metatarsals, and proximal phalanges. An MRI scan showed signal alteration and hypointensity on both T1- and T2-weighted sequences. A three-phase bone scan with Tc-99m-MDP scintigraphy demonstrated moderately intense uptake of the radiopharmaceutical localized to the left lateral foot, which corresponded to the sclerosing lesion seen on the plain radiographs and MRI.

DIAGNOSIS:

Melorheostosis of the left foot.

The plain radiographs showed flowing hyperostosis and candle-wax-like thickening of the cortices involving the third through fifth metatarsophalangeal joints, proximal phalanges, and calcaneus of the left

foot. Three-phase bone scintigraphy demonstrated increased vascular flow and blood pool activity, with associated significant osseous uptake on delayed static images involving the lateral half of the left foot extending from the proximal metatarsophalangeal joints to the calcaneus. MRI showed hyperostosis with uniform hypointensity on all imaging sequences involving the calcaneus and third, fourth, and fifth digits. The pathology report confirmed the clinical and imaging diagnosis and revealed extensive bone remodeling showing both osteoclastic and osteoblastic activity, with associated ossification of fibrous tissue filling the trabecular space consistent with melorheostosis.

DISCUSSION:

Melorheostosis is a rare form of mixed sclerosing bone dysplasia. The name is derived from the Greek term melos (limb) and rhein (to flow). In children, it is characterized by dense linear streaks, mostly in the inner cortex of the affected bones. In adults, irregular ossification is seen along the outer cortex, mimicking candle drippings. Patients with melorheostosis may develop secondary symptoms related to limitation of motion, joint fusion, or periosteal irritation.1,2 The etiology is obscure but Murry and McCreide3 suggested that an infection associated with nerve roots may be responsible for this rare condition. They found that the disorder most often involves one or more segmental sclerotomes, areas of a bone innervated from an individual spinal sensory nerve. This may in part explain the monomelic and linear track involvement and distribution of melorheostoses.

A well known feature of hyperostotic bone remodeling is its distinctive appearance, resembling wax melting and dripping down one side of a candle. Several cases of this sign have been reported from antiquity; the skeleton of a 50-year-old Alaskan Eskimo from the fifth century A.D. and a 25- to 30-year-old female dating back to 4000 to 5000 B.C. from Northern Chile both showed hyperostotic lesions resembling candle wax.4 Despite this characteristic feature, atypical presentations, particularly forme fruste lesions, raise uncertainties about the diagnosis. Forme fruste lesions are considered the mildest manifestation of this condition, which may only focally involve the bone (monostotic) and, as such, is difficult to differentiate from a focus of myositis ossifications or periosteal osteosarcoma.5

Melorheostosis can be found in all age groups but is most frequently diagnosed in young adults. Contracture of joints, fibrosis of soft tissue, and changes in the skin may be present at birth,6 but in these cases definitive diagnosis generally is delayed until osseous abnormalities appear. There is no sexual predilection in the disorder. In 70 to 80% of cases, melorheostosis is monomelic and affects one or more contiguous bones.7 It is more common in lower extremities and is usually appendicular. Other possible sites include the skull, spine, ribs, and pelvic bones.8,9 The disorder usually is asymptomatic in children; in adults, it presents with osseous complaints, usually beginning in the second and third decades of life. Occasionally, it may present with one or more palpable masses. Most of the clinical signs of the osseous dysplasia are associated with fibrosis, which is usually the cause for joint stiffness, angular joint deviations, contractures (mostly flexion), and other orthopedic problems.8,10 Skin pigmentation, scleroderma, and tuberous sclerosis-like thickening have been described.11,12 In rare instances, melorheostosis has been reported in association with tumors such as spinal column lipomatous osteosarcoma, and soft-tissue lesions such as desmoid tumor. Routine laboratory studies usually are unremarkable.

Histologically, sclerosis, soft-tissue fibrosis, and periarticular calcification may be seen, and though these may lead to bony ankylosis of the involved joint, none of these signs are pathognomonic of melorheostosis. Differential diagnosis for this condition includes osteomyelitis, reflex sympathetic dystrophy, neurofibromatosis, soft-tissue sarcoma, and metastatic lesions.

This patient's plain radiographs are characteristic (figure 1), showing wavy cortical hyperostosis which extends along the length of the bone, resembling flowing candle wax. Magnetic resonance imaging (MRI)

(figure 2) features of melorheostosis include hyperostosis, which appears as uniform hypointensity on all imaging sequences. The Tc-99m-MDP three-phase bone scintigraphy image (figure 3) demonstrates moderate to severe increase in tracer in the early and late images, including soft-tissue and blood pool stages of scintigraphy.

The course of this condition is unrelenting; however, it does slow considerably in adulthood. Treatment usually is symptomatic, though surgical measures such as osteotomies, excision, capsulotomies, or tendon lengthening often are pursued.

References

1. Putman CE, Ravin CE: Textbook of Diagnostic Imaging, ed 3, pp 1435-1438. Philadelphia, WB Saunders, 1988.

2. Stark DD, Bradley WG: Magnetic Resonance Imaging, ed 2, pp 2:2152-2156. St. Louis, Mosby-Year Book, Inc., 1992.

3. Murry RD, McCreide J: Melorheostosis and sclerotomes. Skeletal Radiology 4:57-66, 1979.

4. Kelley MA, Lytle K: Brief communication: A possible case of melorheostosis from antiquity. American J Phys Anthropol 98:369-374, 1995.

5. Spieth ME, Greenspan A, Forrester DM: Radionuclide imaging in forme fruste of melorheostosis. Clin Nucl Med 19:512-515, 1994.

6. Young D, Drummond D, Herring J, Cruess RL: Melorheostosis in children. Clinical features and natural history. J Bone Joint Surg Br 61:415, 1979.

7. Kessler HB, Recht MP, Dalinka MK: Vascular anomalies in association with osteodystrophies-

a spectrum. Skeletal Radiol 10:95-101, 1983.

8. Cambell CJ, Papademetrious T, Bonfiglio M: Melorheostosis, a report of the clinical roentgenographic and pathologic findings in fourteen cases. J Bone Joint Surg Am 26:1281, 1968.

9. Ippolito V, Mirra JM, Motta C, et al: Case report 771: Melorheostosis in association with desmoid tumor. Skeletal Radiol 22(4)284-288, 1993.

10. Dissing I, Zafirovski G: Para-articular ossification associated with melorheostosis Leri. Acta Orthp Scand 50:717-719, 1979.

11. Morris JM, Samilson RL, Corley SC: Melorheostosis. J Bone Joint Surg Am 45:1191, 1963.

12. Perlman MD: Melorheostosis: A case report and a literature review. J Foot Surg 29:353,

1990.

Prepared by Amir Salmanzadeh, MD, William Beaumont Hospital, Royal Oak, MI, Stephen J. Pomeranz, MD, Parshan S. Ramsingh, MD, and Jyotsna Rao, MD, Department of Nuclear Medicine, Metabolic Imaging, and Radiology, The Christ

Hospital, Cincinnati, OH.