Abstract
Limb girdle muscular dystrophy type 2B is a rare subtype of muscular dystrophy, the predominant feature of which is muscle weakness. The disease is caused by an autosomal recessively inherited reduction/absence of muscle dysferlin due to a mutation in dysferlin gene at 2p12-14. We report a 10 year old boy who presented with severe non-transient right knee pain and swelling, which later became bilateral. His pain was worst in the morning and during rest. Blood tests revealed markedly raised creatine kinase values (highest 22, 297 U/l), raising the possibility of an inflammatory myositis. MRI showed bilateral asymmetrical muscle involvement of thighs and calves with oedematous changes mimicking the imaging appearances of inflammatory myositis. CRP and ESR levels were consistently within normal limits. Over several months his knee pain worsened and limited walking. Muscle biopsy revealed a severe reduction of dysferlin immunostaining, indicating the diagnosis, which was confirmed by 2 compound heterozygous pathogenic mutations in the dysferlin gene. It is not unusual for this subtype of the disease to mimic myositis: however, significant pain is a rare presenting symptom. Given the significant overlap between this form of muscular dystrophy and inflammatory myopathies, a high index of suspicion is needed to ensure an accurate and timely diagnosis. Furthermore, characteristic inflammatory-related morning pain should not rule out consideration of non-inflammatory causes.
Highlights
Muscle pain is a common presenting symptom to paediatric rheumatology clinics
Limb girdle muscular dystrophies (LGMD) are a rare group of conditions, the predominant feature of which is weakness of lower and upper limbs, symptoms may predominate in one muscle group
We report an atypical case of LGMD type 2B presenting at the age of ten years with significant, nontransient knee pain which was worst in the morning
Summary
Muscle pain is a common presenting symptom to paediatric rheumatology clinics. The overlap between differential diagnoses can sometimes make such cases challenging. He was admitted to hospital following worsening of his knee pain At this point he reported increasing difficulty standing up and needed help getting dressed and getting into the bath due to lower limb muscle weakness. Accurate assessment of strength was difficult because of pain and cooperation; he appeared weak in the lower limbs with 3/5 power in his quadriceps, timed rise from floor sitting position was 1.03 seconds and timed rise from lying was 1.5 seconds (both without a Gower's manoeuvre), both of which were within the normal range He had tight long flexors of his arms, hamstrings and gastrocnemius, but no swelling or restriction of his joints. During neuromuscular examination right lower limb assessment was limited by significant right knee pain and he was agitated due to pain He was able to stand on his left leg but was incapable of maintaining his balance. The mainstay of symptom control included regular non-steroidal analgesics and management by the pain control team
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