Inclusion body myositis (asymmetric distal-proximal LMNL, intact sensation)

Question 1

Inclusion body myositis (IBM) is a progressive inflammatory myopathy.
Characterized by: chronic muscle inflammation and degenerative changes with intracellular protein accumulation.

Presents as:
1. Distal to proximal asymmetric muscle weakness and wasting
2. Reduced reflex (atrophy)
3. Intact sensation
4. Eventual dysphagia, with sparing of EOM

Question 2

Epidemiology: affects older adults, usually over the age of 50.

Question 3

Differential diagnosis of distal to proximal weakness and wasting (LMNL pattern)

Answer 3

1. Motor neuron disease - mixed UMN and LMN
2. AIDP or CIPD (depending on onset) - symmetric, true hyporeflexia
3. Multifocal motor neuropathy - no proximal involvement
4. Myopathies
   - Polymyositis and dermatomyositis - proximal symmetric, heliotrope rash
   - Myotonic dystrophy - myotonia, balding, cataracts
   - FSHD - facial weakness, scapular winging
5. Metabolic, toxic and mitochondrial
   - Pompe disease - proximal weakness
   - Statin induced - proximal weakness
   - Steroid induced

Question 4

Clinical features of inclusion body myositis

Answer 4

1. Middle age adults > 50 years old
2. Insidious slow asymmetric muscle weakness
   - Distal weakness in early: hand and finger weakness - difficult grip, turning keys, buttoning shirt
   - Proximal lower limb weakness (quadriceps): unable to get up from chair, climbing stairs
   - Ambulatory assistance in late stage
3. NO myalgia
4. Dysphagia with NO facial weakness

Question 5

Pathophysiology of inclusion body myositis
1. Clonal expansion of CD8+ T cells and invasion of muscle fibre causing endomysial inflammation
2. Increased MHC-1 molecule expression
3. Histology: mitochondrial abnormalities - rimmed vacuoles with amyloid related proteins
4. Cytoplasmic protein aggregates, accumulation of tau, ubiquitin and mishold proteins
(Inclusion body)

Question 6

Investigations for inclusion body myositis

Answer 6

1. Diagnostic: muscle biopsy - endomysial inflammation, inclusion bodies
2. Elevated CK and anti-cN1A
3. Electromyography - mixed myopathic and neurogenic changes (short duration, low amplitude)
4. MRI of forearm muscles, quadriceps (brain and spinal cord TRO other causes)

Question 7

Management of inclusion body myositis

Answer 7

1. Multidisciplinary: PT, OT, ST, assistive device, neurology
2. Steroids and immunosuppressives are ineffective
   - Long term steroids may worsen myopathies

Question 8

What is the prognosis for individuals diagnosed with Inclusion Body Myositis?

Answer 8

The prognosis is generally poor, with progressive muscle weakness leading to significant disability over time.
Assistive device required after 5-10 years