A Unique Case of Melorheostosis Presenting with Two Radiologically Distinct Lesions in the Shoulder

Melorheostosis is a rare, nonhereditary, benign, mesenchymal condition of unknown aetiology affecting the bones and surrounding tissues. A male patient complaining of left shoulder pain, swelling, and mildly limited range of motion has an exclusive combination of the classic dripping wax lesion in the scapula and the myositis ossificans-like lesion in the deltoid muscle; this combination is the first to be reported in the shoulder. Both lesions showed typical findings of melorheostosis in radiographs, CT, MRI, and bone scan. This case has a stationary course over the follow-up period, and no specific treatment is needed in due course.


Introduction
Melorheostosis is a rare, nonhereditary, benign, mesenchymal condition of unknown aetiology a ecting the bones and surrounding tissues [1]. e incidence is not truly known but has been estimated to be 0.9 per 1,000,000 [2]. e etymology of melorheostosis derives from the Greek terminology-melos [limb], rhein [ ow], and osteos [bone] [3]. It is characterized by cortical bone thickening resulting in irregular hyperostosis that appears to ow down the length of the bone [4]. Radiologically, the appearances are often compared with dripping candle wax, and for this reason, the condition is sometimes referred to as candle disease of the bone [5]. We present a unique case of melorheostosis presenting with two radiologically distinct lesions in the shoulder joint.

Case Report
A 51-year-old male presented to our clinic with a painful swelling in his left shoulder. e pain started gradually ten months before presentation and was progressive in nature.
ere was no history of trauma. e swelling had been gradually increasing in size over a period of three weeks after which growth became static. e pain was provoked by activities requiring shoulder elevation and abduction. Shoulder rotation did not provoke pain. e patient has no clinically relevant past medical or family history.
On examination, a swelling was identi ed in the anterosuperior aspect of the left shoulder with redness of the skin overlying it. e swelling was rm, localised, and mildly tender. e patient demonstrated almost full range of motion with mild pain in abduction and internal rotation (impingement and the Hawkins test were positive) with negative tests for biceps tendonitis, rotator cu tear, AC joint arthritis, and instability.
Radiographs demonstrated calci cation around the greater tuberosity and subacromial space as well as hyperostotic lesions in the scapula blade ( Figure 1). A CT scan revealed extensive yet well-de ned ossi cation within the proximal deltoid muscle and hyperostotic masses dribbling from the scapular blade ( Figure 2). An MRI scan showed a large volume of low-signal intensity calci c foci within and beneath the deltoid muscle with no intra-articular involvement or extension to the proximal humerus itself. ere were also multiple areas of cortical thickening of the scapula ( Figure 3). Otherwise, all structures are normal. Tc-99m MDP bone scan revealed increased uptake in the lesions in the left shoulder, indicating high-grade osteoblastic activity. No other site of abnormal tracer activity was identi ed. ese ndings are consistent with isolated melorheostosis localised to the shoulder region.

Discussion
Melorheostosis was described for the rst time in 1922 by Leri and Joanny [6]. It is characterized by hyperostotic linear bone densities and soft tissue contractures and ossi cation [7]. So far, 313 and 223 cases have been reported in the international and Chinese literature, respectively [5]. e reported age range of presentation for melorheostosis is between 1 and 63 years of age [8], which is consistent with our patient's age. Our patient presented with a monomelic distribution in his left shoulder. ere are con icting reports about the prevalence of monomelic versus polyostotic distributions of melorheostosis [5,8]. However, it is clear that lower limb involvement is more common than upper limb, rib, and spinal involvement [5,8] and that the hands [7] are more frequently a ected than the shoulder in upper limb cases [3,5,[8][9][10][11][12][13].
Several theories to explain the pathogenesis of melorheostosis have been proposed. In 1979, Murray and McCredie [14] suggested that an early embryonic abnormality of a spinal sensory nerve a ecting a single sclerotome resulted in bony overgrowth. is theory is consistent with our patient who has a left scapular blade lesion con ned to the C6 sclerotome as well as with many other cases reported in the literature. It has been suggested that the skin and soft tissue involvement seen in many cases may result from trauma to the corresponding dermatome or myotome [14]. In 1995, Fyns hypothesised that mosaicism was responsible for the development of melorheostosis involving a postzygotic mutation of the mesenchyme resulting in concomitant bony, cutaneous, vascular, and soft tissue involvement. Surprisingly, the soft tissue ossi cation with the redness in the skin and the bony lesion of the scapula in the shoulder of the presented case can be easily explained by this theory [15].
Some studies have attempted to investigate the genetic origin and inheritance pattern of melorheostosis [16]. e LEMD3 gene which encodes for the inner nuclear membrane protein is responsible for controlling bone growth, and mutations in this gene can lead to a proliferation of hyperostotic lesions. Germline LEMD3 mutations were found in patients who had melorheostosis associated with Buschke-Ollendro syndrome (BOS) or Osteopoikilosis [17,18]. However, LEMD3 mutations have never been identi ed from lesional tissue from isolated cases of melorheostosis [18].
Melorheostosis in adults has four distinct radiological appearances in the X-ray: the classic dropping wax appearance, osteoma-like lesion, myositis ossi cans-(MO-) like lesion, osteopathia striata-like lesion, and mixed picture [3]. Children with melorheostosis have di erent radiological pictures [8]. To our knowledge, our case has a unique combination of a classic lesion in the scapular blade and a myositis ossi cans-like lesion in the deltoid muscle. e typical hyperostotic lesion is present in most cases involving the shoulder [1, [9][10][11][12][13]. However, no published cases are   Case Reports in Orthopedics reported on the combination seen in our patient [5,8].
Di erentiating between MO and MO-like melorheostosis lesions is essential. Trauma usually precedes MO, and nodular calci cation is seen in radiological studies for melorheostosis rather than the original lamellar pattern [3,16]. Furthermore, a bone scan of a patient with melorheostosis will demonstrate a signi cantly higher tracer uptake than that would be seen in a patient with MO [28]. Computed tomography [CT] and magnetic resonance imaging [MRI] scans have a supporting role in diagnosing melorheostosis, CT commonly shows high attenuation cortical thickening occluding the medulla, and clear linear demarcation is seen between the lesion and the healthy bone. Soft tissue lesions are easily identi ed on CT. A degree of mineralisation is seen, and often the soft tissue lesions are not in continuity with the bone [10,16]. e CT scan of our patient demonstrated this classic presentation.
MRI of bone lesions in melorheostosis shows low signal intensity on all pulse sequences encroaching on the medullary canal which is typical for the scapular lesion of the case presented. Soft tissue lesions produce heterogeneous MRI patterns according to the degree of mineralisation. Low signal intensity is detected in mineralised lesions as is shown in our case. Intermediate to high signal is predominantly in the nonmineralised lesions [10,16,20].
Since 1976, Tc-99m bone scintigraphy has been developed as a tool to con rm the diagnosis of melorheostosis and unveil other silent lesions [29,30]. Melorheostosis causes increased tracer uptake, which bridges over the joints due to hypervascularity, which has been con rmed by angiographic studies [16,28]. e reduced tracer uptake observed in patients treated with bisphosphonates supports the theory that increased osteoblastic activity and turnover are key processes occurring in melorheostosis [9,23].
In this case, based on our ndings, we concluded that this is a case of isolated melorheostosis. e common differential diagnosis of melorheostosis includes myositis ossi cans, synovial osteochondromatosis, osteoma, parosteal osteosarcoma, focal scleroderma, and Ca ey disease. Combined clinical examination and full radiological workup can accurately di erentiate diagnoses. Osteoma presents with a smooth outline, focal, single vertebral involvement in the spine. Ca ey disease a ects infants with lamellated periosteal reaction, transient and less dense. Classic cauli ower-like ossi ed mass characterises parosteal osteosarcoma, a lucent line between lesion and cortex, increased uptake on bone scan. Osteopathia striata may be mistaken for melorheostosis, but striations in melorheostosis are much larger, broader, and unilateral, unlike the genuine osteopathia striata. Osteopoikilosis has numerous round to ovoid white densities of similar size spread throughout all bones; approximately 10% of osteopoikilosis is accompanied by skin elastic or collagen nevi, named as BOS. Tumor cacinosis is usually associated with a systemic disorder of calcium metabolism or renal dialysis, presents bilaterally and causes erosion of cortex, amorphous and cystic multilobulated calci cation in periarticular distribution. Calcium pyrophosphate dihydrate deposition (CPPD) disease a ects the elderly; with a characteristic a nity to ligamentum avum and synovial joints of the spine is in ligamentum avum and synovial joints [7,19].
ere is no standard treatment for melorheostosis, and management plans must be made on an individual patient basis [8]. e aims of treatment are pain relief and maintaining function.
ere are a few reports describing successful analgesia with the use of bisphosphonates [9,23]. Surgical procedures may be o ered to patients experiencing mechanical symptoms such as nerve compression, contractures, impingement, and deformity [7,12,21,22,27].
We have followed our patient over six months, and radiologically, the ndings are stationary. Clinically, pain has settled down, and he has nearly no mechanical symptoms, thus no rationale for any intervention in the meantime.

Conclusion
Our patient has a unique presentation of melorheostosis presenting with two distinct coinciding lesions in the shoulder joint. Our case supports existing theories regarding the aetiology of the disease and contributes to the literature on the spectrum of possible presentations of melorheostosis.

Consent
Consent was obtained.

Disclosure
An earlier version of this case was presented at Cairo at the Annual Conferences of the EOA: "http://www.eoa.org. eg/2016/program/d1.htm."

Conflicts of Interest
e authors declare that there are no con icts of interest regarding the publication of this article.

Authors' Contributions
Ahmed A. Elsheikh has examined the patient with the fourth author and written the body of the report and the discussion Case Reports in Orthopedics (50%). Rohan S. Pinto has written the introduction and modi ed and revised the whole manuscript (20%). Alpesh Mistry has revised the radiological review and approved the report (20%). Simon P. Frostick has revised and approved the nal version of the report (10%).