Chapter 12: MUSCULOSKELETAL DISORDERS

Student Authors: Carol Naidoo, Lehlohonolo Ntlatlapo, Sean Mashau and Dyavan Singh

Specialist Advisor: Dr Chantel Richardson

chapter 12 dermatology image

This chapter covers the following topics:

JUVENILE IDIOPATHIC ARTHRITIS (JIA)

It is a chronic (<6 weeks duration) inflammatory condition which develops in children >16 years old. It develops in the absence of infection and has no known cause.

Pathogenesis

The pathogenesis of JIA is unclear, however there are multiple factors that interact and contribute to its development:

Clinical Features

Generally, the child with JIA may present with:

Investigations

One should order:

Classification of JIA

There are at least six different subtypes of JIA:

Table 12.1: Classification and Features of JIA

JIA Subtype Age of Onset Sex ratio (F:M) Articular pattern Extra-articular features Laboratory Findings
Oligoarticular JIA 1-4years 4:1 Involves ≤4 joints (usually knee, ankle or wrist). >4 joints may be involved after 6 months (extended oligoarticular arthritis) Chronic anterior uveitis (in 20% of cases) and leg length discrepancy 70% of patients are ANA-positive. Acute phase reactants (APRs) and platelets may be raised
RF-positive polyarthritis 1-3 years 3:1 Involves the small joints of the hand (including the distal interphalangeal (DIP) joints Iridocyclitis APRs and platelets are elevated RF-negative but ANA-positive in 40% of cases
RF-negative polyarthritis Late adolescence 6:1 Widespread joint involvement Symmetrical small joint involvement but with sparing the metacarpophalangeal (MCP) joints. Iridocyclitis is not a feature. Elevated APRs, anaemia, RF-positive (on two occasions) and anti- CCP-positive.
Systemic JIA 1-10 years 1:1 Initially no arthritis (just arthralgia or myalgia), but then oligo- or polyarthritis. Fever with evanescent rash, lymphadenopathy, serositis and hepatosplenomegaly. Raised APRs, neutrophilia, thrombocytosis and anaemia. RF-negative.
ERA 6-16 years old 1:7 Arthritis or enthesitis of the sacroiliac joint, inferior pole of patella, Achilles tendon or plantar fascia insertion into the calcaneus. Sacroiliitis or lumbosacral pain, first-degree relative with ERA or ankylosing spondylitis and anterior iridocyclitis. HLA-827-positive, elevated ESR and anaemia.
Psoriatic arthritis 1-16 years old 2:1 Similar to oligoarthritis
  1. Dactylitis
  2. Nail abnormalities
  3. Family history of psoriasis
  4. Iridocyclitis
 RF-negative. Half of patients are ANA-positive.

Management

Non-Pharmacological Management

The patient, his/her parents and teachers must be counselled and educated on the condition. Referrals to a physiotherapist and occupational therapist should be made.

Pharmacological Management

The patient should be prescribed:

If symptoms and signs are not controlled on the above treatment, one should prescribe disease-modifying anti-rheumatic drugs (DMARDs) e.g. methotrexate 0.4 mg/kg orally or subcutaneously. If control is still not gained, refer for specialist opinion (will likely start biological agents e.g. anti-tumour necrosis factor/TNF).

Complications

They may include:

IN-TOEING/PIGEON-TOEING

Pathophysiology and Aetiology

The abnormal positioning of the leg may be due to:

Thus, the cause of the in-toeing may be at the hips, legs or feet, respectively

Clinical Features

The child will have his/her:

‘W’ sitting position is more comfortable for the child.

Management

It is rarely treated. However, one may offer:

GENU VALGUM (KNOCK KNEES)

Aetiology

Genu valgum may be part of normal growth and development or it could be a sign of an underlying bone disease e.g. osteomalacia, rickets (due to a lack of calcium, phosphorus or vitamin D). Occasionally, it may be the result of injury to the tibial growth plate. It is important to differentiate the above mentioned causes from obesity-related genu valgum. However, obesity can worsen genu valgum in patients with any of the abovementioned causes.

Clinical Features

When standing, the child’s knees will touch (symmetrically lean inward) but the ankles will not touch (in a child with an average weight). This is best seen with the child’s toes pointed forward.

Management

Management may be:

GENU VARUM (BOW LEGS)

Pathophysiology

It is mostly physiological in children under 2 years. However, it may be the result of an underlying condition e.g. Blount’s disease (caused by an abnormality of the tibial growth plate), rickets.

Clinical Features

Either or both legs may be affected. The child will have a distinct space between the lower legs and knees when standing with his/her feet together. This bowing is exaggerated by walking (see related image here). Adolescents with Blount’s disease will have pain associated with the bowing.

Investigations

One may perform:

Management

It may be:

SEPTIC ARTHRITIS

It is a serious infection as it can lead to bone destruction. Infection of the joint can be caused by bacteria, fungi, viruses or mycobacteria.

Pathophysiology and Aetiology

It is most common in children <2 years old and usually spreads to the joint:

S aureus is the most common cause of septic arthritis. Organisms implicated in neonatal septic arthritis are group B streptococci, N. gonorrhoea and Gram-negative bacilli.

Clinical Features

The child may present with a history of trauma or underlying osteomyelitis. On examination, one may find:

Note: If more than one joint is involved, then the diagnosis of septic arthritis needs to be reviewed.

Investigations

They should include:

Management

Diagnosis and management should be carried out quickly and efficiently to prevent long- term damage to bones and joints. The child should be managed in conjunction with an orthopaedic surgeon. Management includes:

OSTEOMYELITIS

.It is inflammation of the bone and is usually caused by bacterial infection (see related image here).

Pathophysiology

In children, the infection is spread haematogenously but can be spread from other sources as well. This is because there is a rich vascular supply to the bones as they are still growing. Circulation within the metaphyseal capillary loops is sluggish, which is why infection tends to start there. Commonly affected bones include the femur, tibia, and humerus.

Aetiology

Common causative organisms include S. aureus, S. pneumoniae and S. pyogenes. Other causes include Pseudomonas aeruginosa, fungi (in the immunocompromised patient), Salmonella sp (in sickle cell anaemia and other haemoglobinopathies).

Clinical Features

The child may have:

Investigations

One must exclude cellulitis, subcutaneous abscess, fractures and bone tumours. Thus, the following investigations are done:

Management

The patient should be started on antibiotics (after taking samples for the lab). Cloxacillin is usually given or vancomycin may be given if the child has a penicillin allergy.

SYSTEMIC LUPUS ERYTHEMATOSUS (SLE)

SLE is an autoimmune, inflammatory condition that leads to the damage of essential organs. Its natural history is unpredictable as patients may present with chronic symptoms or acute life-threatening disease. Its cause remains poorly understood.

Clinical Features and Complications

The child may present with:

See related image here.

Diagnosis

The Systemic Lupus International Collaborating Clinics (SLICC) Classification Criteria are used to diagnose SLE. For the diagnosis to be made, the patient must have:

Table 12.2: SLICC Classification Criteria

Clinical Criteria Laboratory Criteria
  • Acute cutaneous lupus
  • Chronic cutaneous lupus
  • Oral or nasal ulcers
  • Nonscarring alopecia
  • Arthritis
  • Serositis
  • Renal dysfunction
  • Neurological symptoms
  • Haemolytic anaemia
  • Leukopenia
  • Thrombocytopenia (<1 000 000/mm3)
  • Positive ANA
  • Positive anti-dsDNA
  • Positive anti-Smith antibodies (anti-Sm)
  • Positive antiphospholipid antibodies
  • Low complement (C3, C4 or CH50)
  • Positive direct Coombs test (unreliable in the presence of haemolytic anaemia)

Investigations

See table 12.2 above for guidance on which investigations to order.

Management

The patient should be referred to a tertiary care facility. Management depends on the organ involved and the severity of its involvement. Non-pharmacological management includes dietary restrictions driven by the patient’s medical therapy and pharmacological management ranges from NSAIDs and steroid therapy to cyclophosphamide.

CONGENITAL MYOPATHIES

Congenital myopathies are a heterogenous group of primary muscle disorders. Although they are present from birth, their expression may be delayed.

Pathophysiology

In these children, the muscle fibres do not function properly, leading to muscle weakness and/or hypotonia. The weakness is either stable or slowly progresses.

Clinical Features

The child may present with:

In some cases, distal muscles are affected, however myopathy usually affects proximal muscle more than distal muscles. Respiratory muscle is almost always affected. This usually occurs later in the disease.

Investigations

One should perform

Management

Although there is no known cure for congenital myopathies, symptomatic management is offered and patients should have regular consultations with specialists (such as orthopaedics and pulmonologists) to assess the progression of the disease. Rehabilitation with physiotherapists, speech and language pathologists and occupational therapists can help manage symptoms. Low-impact exercises can help maintain muscle bulk and strength e.g. swimming, walking.

DUCHENNE MUSCULAR DYSTROPHY (DMD)

It is an X- linked recessive disorder that results in progressive degeneration of muscle (see related image here).

Pathophysiology

Dystrophin connects the cytoskeleton of a muscle fibre to the extracellular matrix through the cell membrane. In DMD, there is a deletion in the dystrophin gene. It results in myofiber necrosis with an elevated creatine kinase (CK).

Clinical Features

The history may allude to the fact that there is a familial pattern of DMD. The child may present with:

These children have decreased life expectancies because of respiratory failure or associated cardiomyopathy. Due to the progressive nature of the disease, the average age of diagnosis is 5 years old and most children are no longer ambulant by 10-14 years old.

Investigations

They should include

Management

The child should be managed by a multidisciplinary team:

Due to the respiratory muscle weakness, children with DMD may develop nocturnal hypoxia and may require overnight CPAP to improve breathing. Glucocorticoids may be prescribed as they also help preserve mobility and prevent scoliosis. However, their exact mechanism of action is not known. Glucocorticoids have also been shown to benefit cardiac muscle function.

PERTHES DISEASE

It is more common in males (M:F = 5:1) and mainly affects children 5-10 years old.

Pathophysiology

There is avascular necrosis of the epiphysis of the femoral head due to loss of the blood supply. This is followed by revascularisation and re-ossification.

Clinical Features

They are usually insidious. The child will usually present with hip or knee pain and/or limp of acute onset. The disease is bilateral in 10-20% of cases.

Investigations

One should request a frog-leg lateral X-ray of both hips. The X-ray will show increased density, flattening, sclerosis and fragmentation of the femoral head.

Management

It includes rest, physiotherapy (to increase hip movement) and, in some cases, traction, casts or surgery.

SLIPPED UPPER FEMORAL EPIPHYSIS (SUFE)

It is defined as displacement of the femoral epiphysis from the femoral neck along the physeal plate.

Aetiology

The displacement is caused by a force exerted on the femoral head which exceeds the strength of the femoral physis. Factors which contribute to the weakening of a weak femoral physis include:

Clinical Features

The child may present with limb or hip pain which may be referred to the knee. On examination, one will find restricted abduction and internal rotation of the hip.

Investigations

A frog-leg lateral X-ray of the hips will show the slipped upper femoral epiphysis.

Management

These patients are managed surgically with pin fixation.

JUVENILE DERMATOMYOSITIS (JDM)

It is an autoimmune myopathy which is primarily caused by a capillary vasculopathy. It is 2-5 times more common in females than males.

Pathophysiology and Causes

JDM is associated with systemic vasculopathy and is sometimes associated with occlusive arteriopathy and capillary necrosis, which eventually lead to capillary loss and tissue ischemia. As with adult dermatomyositis (see images of dermatomyositis here and here, it is likely an antibody-dependent, complement-mediated disease in which capillary injury results in muscle fibre atrophy. Although the aetiology remains unclear, it has been proposed that JDM is caused by an autoimmune reaction in genetically susceptible individuals, possibly in response to infection or environmental triggers e.g. prenatal exposure to tobacco smoke and particulate inhalants. Thus, it may be the result of:

Clinical Presentation

The child will present with:

Investigations

One should perform:

Management

Mild-to-moderate disease may be managed with oral prednisone or steroid sparing drugs e.g. methotrexate. Severe or life-threatening disease may be managed with IV methylprednisolone or IV cyclophosphamide.