Distinguishing hereditary forms of
myopathy from certain forms of
inflammatory myopathy can be challenging. We present 3 cases where a certain degree of overlap was observed between genetics and autoimmunity. A child with
juvenile dermatomyositis where heterozygosity for a pathogenic mutation implicated in
LGMD1C resulted in a delayed diagnosis. A young lady with anti-SRP positive insidious proximal
polymyositis worsening post-partum, diagnosed eventually as
LGMD2. An adolescent child referred for proximal
myopathy in view of paternal history of
LGMD2 but found to have signs of
systemic sclerosis with overlap
myositis with excellent recovery on
therapy. While improvements in whole genome sequencing and detection of
myositis specific
antibodies have revolutionised the diagnosis and treatment of these diseases, they are still not robust enough and may cloud good clinical judgement in accurate diagnosis and management. Higher sensitivity of these assays is bringing to the fore the possibility that these diagnoses may not be mutually exclusive and might plausibly be concurrent, pending further investigation. These are three interesting cases depicting the difficulties frequently encountered by rheumatologists and neurologists in distinguishing inflammatory from genetic
myopathies.