
Hypothyroid	Weakness without cramps or myalgias Sluggish reflexes with delayed relaxation CK elevation can occur Rhabdomyolysis very rare
Hyperthyroid	Proximal weakness, cramps may occur but rare Normal or Increased reflexes CK rarely rises
Cushings	Proximal muscle weakness with atrophy CK normal
Hypokalaemia	Proximal weakness Myalgias rare Acute or chronic CK normal or slight elevation
Critical illness myopathy (usually after steroid use)	Flaccid quadriparesis CK elevated in 50%
Polymyositis	Proximal weakness Mild to moderate myalgias in up to 50% Atrophy late in disease CK elevated in 95% LD in 90% AST/ALT in 85%
Statin induced	Myalgias common CK elevation common Rhabdomyolysis rare unless co-existing condition or other drugs co-administered

Dystrophies

Muscular dystrophies

Congenital Myopathies

Definition

· Present at birth.

· Progress little or not at all.

· Specific morphological abnormalities visible on muscle biopsy.

Clinical features – general

· Myotonia congenital (floppy infant)

· Proximal weakness lower limbs >upper limbs

· Occasional extraoccular and facial involvement

· Face and head narrow and high (dolichocephaly)

· Often co-existent deformities – pectus excavatum, scoliosus, hip dysplasia, pes cavus, pes planus, clubfoot.

· Reflexes normal or diminished

· Cardiomyopathy rare

· Reduced life expectancy is the rule

· Occaional mental retardation

Investigations – general

· CK usually normal or mild elevation

· EMG myopathic

· Muscle biopsy – usually diagnostic with specific features.

Types:

· Central core disease

Namaline myopathy
Centronuclear Myopathy
Multicore
Fingerprint body myopathy
Sarcotubulat
Hyaline body myopathy

Metabolic Myopathies/Storage Disorders

Glycogen storage defects

Acid Maltase Deficiency

· Autosomal recessive

Clinical features

Infant onset

· Floppy infants

· Enlargement of

o Liver

o Heart

o Tongue

· Respiratory insufficiency

· Dysphagia

· Life expectancy of less than 2yrs

Adult onset

· Progressive proximal weakness

· Respiratory insufficiency

· Can present similarly to limb girdle or scapuloperoneal muscular dystrophy

Investigations

· CK mildly elevated

· EMG – myopathic, CRDs

· Lactate rises with ischaemia test

· Muscle biopsy

o Glycogen –laden vacuoles and lysosomes

Lipid disorders

Carnitine Palmitoyltransferase Deficiency
Myoadenylate deaminase deficiency

Mitochondrial Myopathies

Kearns-Sayre Syndrome
Progressive External Opthalmoplegia
Autosomal recessive cardiomyopathy and opthalmoplegia (ARCO)
Myoclonic Epilepsy with Ragger Red Fibres (MERRF)
Mitochondiral Myopathy, Encephalopathy, Lactic Acidosis and Stroke-like Episodes (MELAS)

Muscle Membrane Disorders

Hypokalaemic Periodic Paralysis
Hyperkalaemic Periodic Paralysis
Paramyotonia congenita

Drug induced Myopathies

Statin associated myopathy

Three types of muscle issues with statins:

· Myalgia

· Rhabdomyolysis

· Immune mediated necrotizing myopathy

Myalgia

· Many meta-analysis do not suggest a significant increase, however many poorly conducted studies

· Well conducted STOMP study

o 9% of patients had myalgia, none had impaired strength or exercise function

o ~20% of all patients had a minor elevation in CK

o None had elevation >10x ULN

o CK and myalgia do not always go together

o Myalgia with statins tended to be lower limbs – proximal and calves. Myalgia on placebo more generalised.

· If >5x ULN consider ceasing to see if CK returns to normal (if not there may be another cause)

Rhabdomyolysis

· Rare – exact incidence unknown

· High dose is a risk factor.

· Co-use with medication that increases statin concentration may be a risk factor (e.g. erythromycin, ciprofloxacin, azole anti-fungals, fibrates, calcium channel blockers, Ciclosporin)

· Not an absolute contra-indication to restarting statin, although probably at a lower dose.

Immune mediated Necrotizing Myopathy

· See other topic

Statins with pre-existing muscle disease

· Case reports only of worsening

· Possible worsening of myasthenia in some reports

· Possible reports in patients with mitochondrial myopathy

· Start low, record CK first and monitor regularly.

Reference: Statin related myopathies, Hilton-Jones, Practical neurology 2018.