The ABCs of MHE

 

 

 

 

Harish Hosalkar, MD.; John Dormans, MD., Chief of Orthopedic Surgery, Children’s Hospital of Philadelphia,  Professor of Orthopaedic Surgery, University of Pennsylvania School of Medicine;  Notes from The MHE Coalition

 

Diagnostic Tools

 

Important features of orthopedic exam: It is important to follow each step of the exam during every office assessment of MHE patients.

 

  • Patient should be comfortable with adequate exposure and well-lit surroundings (lest some important physical finding is missed).

  • It is important to assess how the patient moves about in the room before and during the examination as well as during various maneuvers. Balance, posture and gait pattern should also be checked.

  • General exam findings should look for any lumps and bumps that can be felt on any anatomical sites that can be easily palpated. Chest wall, abdominal and deep pelvic exam should be performed in all cases. Sessile or pedunculated nature of the bumps should be ascertained if possible.

  • General body habitus, including developmental milestones should be noted

  • It is important to note any obvious spinal asymmetry, deformities, trunk decompensation, and evidence of para-spinal muscle spasm or elevation suggestive of spinal lesions.

  • The patient’s height should be measured and monitored on subsequent visits. Individuals with MHE are frequently of short stature, with most having heights 0.5 to 1.0 SD below the mean. (The lesions tend to enlarge while the physes are open proportionate to the overall growth of the patient, and the growth of the osteochondromas usually ceases at skeletal maturity). 

  • It is essential to perform and document a thorough neurologic exam. Asymmetric abdominal reflex is a subtle sign of spinal pathology and may be associated with spinal cord compression. Motor, sensory and reflex testing should be performed and recorded.

  • Any discrepancies in limb lengths should be noted and evaluated as femoral, tibial or both.

  • Arm, forearm, thigh and leg girths should be recorded especially so when an obvious difference is noted on clinical exam.

  • Any deformities should be noted and recorded. The most common deformities seen in MHE include short stature, limb-length discrepancies, valgus deformities of the knee and ankle, asymmetry of the pectoral and pelvic girdles, bowing of the radius with ulnar deviation of the wrist, and subluxation of the radial head.

  • The range of motion of all joints, their stability, and any evidence of hyperlaxity, should also be noted in all cases.

  • Distal vascular and neurological status (motor, sensory and reflex) should be evaluated and recorded. This includes checking of pulse in hands and feet as well as sensations.

 

Frequency of Follow-up

 

  • Children should be followed up at 6-9 month intervals and sooner if there are any red flags in terms of sudden increase in size of the bump, pain, tingling, numbness, weakness, visible and progressive limp, limb deformities and length discrepancies

 

  • It is important to keep a regular follow-up of all cases even after skeletal maturity. Most patients have increased awareness of all the red flags to be watched for by this time and hence can keep a personal lookout for the same. A thorough exam can be performed by the clinician (including measurements) during the office visit. Radiographs should be repeated only when the bumps are symptomatic or growing.

 

Note: Your child’s orthopaedist may recommend follow-up at different intervals, sometimes every 3 months, sometimes a year or more, and can explain why that time frame is indicated.

 

Characterization of Lesions:

Location: Whether the tumor is located in the limb bones, chest wall or ribs, skull, or any other sites in the body.

  • Pain: Is the lesion associated with pain? If yes:

  • Intensity: Can be assessed and documented in a lot of ways.

i. On a pain scale of 1 to 10.

ii. The MHE and Me Website now features the Bumpy Bone Tracker, Pain Tracker and Pain Diary, all of which can be used as a tool to discuss pain with a child during an examination

  • Quality:

    Do you experience pain on and off (intermittently) throughout the day, or all the time (constantly)?

    Does the pain occur at specific times, or with specific activities (ex. Upon waking in the morning, when walking, etc.)

    Is pain interfering with your general activities?

    Do you need to use special accommodations at work or school?

    Is pain affecting your mood?

    Do you take medications for pain, or use other treatments (i.e. heat, ice, rest).  If so, are these treatments effective?

    Tumor pain is often unrelenting, progressive, and often present during the night.

    Is there any shooting pain? (Suggestive of nerve compression)

  • Radiation: Pain radiating to upper or lower extremities or complaints of numbness, tingling or weakness suggest neurologic compression and requires appropriate workup.

  • Onset:

  • How was the tumor noticed?

  • Was there any history of trauma?

  • When did the pain actually start?

 

  • Duration:

  • What has been the duration of this new lesion?

  • How long have the other lesions been around?

4.   Progress: Whether the exostosis has remained the same, grown larger, or gotten smaller?

5.   Associated symptomatology:

  • Gait and posture disturbances (especially during follow-up of skull or spinal lesions and in cases of limb-length discrepancies and deformities).

  • Any specific history of backpain. If yes, its complete characterization.

  • Change in bladder or bowel habits (for evidence of spinal lesions causing cord compression)

  • Gynecologic function alterations in girls with pelvic lesions.

  • Scoliosis may be associated with spinal lesions and may need to be monitored.

  • Night pain if present is a worrisome symptom and needs complete evaluation. Night pain is different than chronic pain in that the pain is not constant and characteristically wakes the patient from sound sleep. Chronic pain on the other hand is persistent and would interfere with the sleep pattern by making the patient restless. Chronic night pain is especially common in MHE cases where the location of the bump may cause pressure on the exostoses when lying down. Soft beds, air cushions, lateral positioning and frequent turning may prove to be helpful in these cases.

  • Neurologic symptoms may be associated spinal or skull lesions. More commonly, local compression of peripheral nerves due to expanding lesions is encountered in arms and legs. In addition, several cases of Reflex Sympathetic Dystrophy (RSD) following MHE surgeries to knees and wrists have been noted.  Many patients also experience other nerve-related symptoms following surgery, including long-lasting pain and sensitivity around surgical sites long after incisions have healed.

  • Bursa formation and resulting bursitis may occur as a result of the exostoses and should be recorded. A bursa is a fibrous sac lined with synovial membrane and filled with synovial fluid and is found. The function of a bursa is to decrease friction between two surfaces that move in different directions. Therefore, you tend to find bursae at points where muscles, ligaments, and tendons glide over bones. These bursae can be either anatomical (present normally) or may be developmental (when the situation demands).  The bursae can be thought of as a zip lock bag with a small amount of oil and no air inside. In the normal state, this would provide a slippery surface that would have almost no friction. A problem arises when a bursa becomes inflamed. It loses its gliding capabilities, and becomes more and more irritated when it is moved. Bursitis can either result from a repetitive movement or due to prolonged or excessive pressure.

 

Note from The MHE Coalition:  Children who have been experiencing MHE-related pain may be hesitant to share this information with their doctors, fearing that the doctor will recommend surgery.  It is not unusual for children to try to minimize their symptoms.  We advise families to use the pain tracker tools available to keep an ongoing record between check-ups.  It is also important for both parents and physicians to let children know that pain does not necessarily mean surgery, but that it is important to let the doctor know about symptoms they have been experiencing.

 

 
Diagnostic work-up
Physical examination.

A thorough physical examination of the patient is extremely important in the assessment of MHE patients.

 

Radiographs

High quality plain radiographs (X-rays) (anteroposterior and lateral views) should be ordered in cases presenting with exostoses. Standing postero-anterior and lateral views of the entire spine on a three-foot cassette should be ordered when spinal lesions are suspected. Special views like tangential views of the scapula may need to be ordered in some cases. Plain films help to localize the lesion and give a fairly good idea about its size and dimensions in 2 planes. Also scanograms help to assess the extent of limb-length discrepancy and its localization. Oblique views of the spine and special skull views may be ordered in suspected cases.

 

Advanced Imaging

Radionucleide bone scan is sensitive to pathologies causing increased bone activities within the skeleton. In combination with SPECT (single photon emission computed tomography), it gives excellent localization of the area of increased uptake. This is extremely useful in MHE to locate multiple lesions, especially those that are situated in deeper areas not amenable to clinical palpation. Further imaging if required, can then be focused. Thallium and PET (positron emission Tomography) scans are also modalities that can help define the tumor metastasis especially in those rare cases of malignant degeneration.

 

Computed Tomography (CT)

CT scans are useful in visualizing the bony architecture particularly as an adjunct to plain radiographs or bone scans. Thin slice CT cuts may be necessary in small lesions. Two and three-dimensional reconstructions are possible and add to the information. Rarely the CT may be combined with the myelogram to effectively delineate the size of the lesion especially for intraspinal lesions.

 

Magnetic Resonance Imaging (MRI)

This is an excellent modality for defining the spinal cord, nerve roots, soft tissue structures and cartilage.  Cortical bone is not seen as well as compared with CT.  Cartilage caps of the exostoses and their compression effects on soft-tissues, nerves and adjacent vessels can be very well delineated. It is a study of choice in suspected cases of malignant transformation. MRI studies must be reserved for those cases in which clinical signs and symptoms deem them appropriate. Clinicians must make a point to communicate clinical information and suspected differential diagnosis to the radiologists.

 

Other Diagnostic Tools

 

Ultrasound

May be necessary to diagnose compression of arteries. The principle for ultrasound, or ultrasonography, is the same as for underwater sonar or echo sounding. An apparatus sends an ultrasonic wave through the body at a speed of about 1,500 meters per second. At the interface between two types of tissue, the wave will be refracted or ‘broken up’, and part of the wave will be reflected back and detected by the apparatus. The rest of the ultrasonic wave continues deeper into the body, and is reflected as an echo from the surface of tissues lying further inside the body. How much is reflected depends on the densities of the respective tissues, and thus the speed of the sound wave as it passes through them. The time taken for the reflected wave to return indicates how deep the tissue lies within the body. In this way, one obtains a picture of the relative locations of the tissues in the body, in the same way that one may visualize the contours of a school of fish with sonar. An ultrasound can help ascertain the status of the blood flow through the arteries as well and is therefore important for assessment of suspected compression.

 

EMG (Electromyography, myogram)

May be necessary in cases of suspected nerve damage

What is EMG

Electromyography is a test that measures muscle response to nervous stimulation (electrical activity within muscle fibers).

 

How the test is performed

A needle electrode is inserted through the skin into the muscle. The electrical activity detected by this electrode is displayed on a monitor (and may be heard audibly through a speaker). Several electrodes may need to be placed at various locations to obtain an accurate study.After placement of the electrode(s), you may be asked to contract the muscle (for example, by bending your arm). The presence, size, and shape of the wave form (the action potential) produced on the monitor provide information about the ability of the muscle to respond when the nerves are stimulated.

 

Each muscle fiber that contracts will produce an action potential, and the size of the muscle fiber affects the rate (frequency) and size (amplitude) of the action potentials.

A nerve conduction velocity test is often done at the same time as an EMG.

 

Why the test is performed

EMG is most often used when people have symptoms of weakness and examination shows impaired muscle strength. It can help to differentiate primary muscle conditions from muscle weakness caused by neurologic disorders.

 

EMG can be used to differentiate between true weakness and reduced use due to pain or lack of motivation.

 

Histology

Clinical examination and Imaging findings can help establishing the diagnosis in most cases. Biopsy should be performed when a malignant change is suspected.

 

Laboratory evaluation

Genetic linkages to MHE have been documented which form the basis of genetic testing.

 

Test methods:

Sequence analysis of the EXT1 and EXT2 genes are offered as separate tests.  Using genomic DNA obtained from buccal (cheek) swabs or blood (5cc in EDTA), testing of EXT1 proceeds by bi-directional sequence analysis of all 11 coding exons.  The EXT2 gene consists of 15 exons, and all coding exons (2-15) are sequenced in the analysis.

Test sensitivity:

 

In patients with MHE, mutations are found in approximately 80% of individuals. Of those in whom mutations are identified, 70% of the mutations are found in the EXT1 gene and the remaining 30% in the EXT2 gene. Thus, the method used to screen the EXT1 is expected to identify approximately 60% of mutations in MHE. In individuals who are found to be negative on analysis of the EXT1 gene, screening of the EXT2 gene will identify the molecular basis of the disease in a further 25% of affected individuals. To date, there are no known distinguishing features within the clinical diagnosis of MHE known to predict which gene is more likely to have a mutation. Multiple exostoses can be associated with contiguous deletion syndromes, which are not detected with these methods.

 

 

Glossary of terms and procedures:

 

Synonyms of multiple exostoses: A number of synonyms have been used for this disorder including osteochondromatosis, multiple hereditary osteochondromata, multiple congenital osteochondromata, diaphyseal aclasis, chondral osteogenic dysplasia of direction, chondral osteoma, deforming chondrodysplasia, dyschondroplasia, exostosing disease, exostotic dysplasia, hereditary deforming chondrodysplasia, multiple osteomatoses, and osteogenic disease.

Anterior: Situated in the front; forward part of an organ or limb

Ball and socket joints: Movable (synovial) joints, such as hips and shoulders, that allow a wide range of movement.

Bilateral: having two sides or pertaining to both sides.

Biopsy: Take a piece of the lesion to study the histological characteristics.

Cartilage: Form of connective tissue, more elastic than bone, which makes up parts of the skeleton and covers joint surfaces of bones.

Coxa-valga: When the thighbones are drawn farther apart from the midline due to an increase in the neck-shaft angle of the femur.

Coxa-vara: When the thighbones are drawn closer to the midline due to a decrease in the neck-shaft angle of the femur.

Dislocation: When the normal articulating joint surfaces have lost total contact.

Distal:  Away from the midline or the beginning of a body structure (the distal end of the humerus forms part of the elbow).

Epiphysiodesis: To surgically stop the growth of the growing end of the bone either temporarily or permanently.

Excision: To surgically remove the lesion.

Genu-valgum: Knock-knees.

Genu-varum: Bowlegs.

Hinge joints: movable joints, such as knees and elbows, that allow movement in one direction.

Limb-lengthening: Process of increasing the length of bones using one of the various devices.

LLD: Limb-length discrepancy- difference in limb lengths.

Medial: Pertaining to the middle or toward the midline.

MHE: An autosomal-dominant disorder manifested by multiple osteochondromas and frequently associated with characteristic skeletal deformities.

Osteochondromas: Cartilage capped tumors found commonly at rapidly growing ends of bones.

Osteotomy: The surgical division or sectioning of a bone.

Pedunculated: Lesion with a stalk connecting it to the main bone.

Posterior: Situated in the back; back part of an organ or limb

Proximal: Near the midline or beginning of a body structure (the proximal end of the humerus forms part of the shoulder).

Sessile: Lesion without a stalk connecting it to the main bone.

Stapling: Process of insertion of a mechanical device (staple) following surgical intervention.

Subluxation: When the joint surfaces are still facing each other but not totally in contact.

esions are suspected. Special views like tangential views of the scapula may need to be ordered in some cases. Plain films help to localize the lesion and give a fairly good idea about its size and dimensions in 2 planes. Also scanograms help to assess the extent of limb-length discrepancy and its localization. Oblique views of the spine and special skull views may be ordered in suspected cases.

 

Continued...

 

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