P035 Inflammatory myopathy and metabolic disorders causing myopathies
Authors: Malik Mariam , Mason Alice , Davidson Brian , Furby Julian 
Published: April 2021

Background/Aims 

Myopathies due to inborn errors of metabolism can be difficult to differentiate from inflammatory myopathies. Careful history, examination and laboratory tests are required to establish the diagnosis. We present a case of Riboflavin Transport Deficiency (Brown-Vialetto-Van Laere syndrome) masquerading as an inflammatory myopathy.

Methods 

A 37-year-old lady presented with severe proximal muscle weakness. She had background of sensory neuropathy and chronic anaemia. Notably, her sister had a history of similar symptoms. Creatine Kinase (CK) was 360 IU/L and lactate dehydrogenase (LDH) was 1700 IU/L. Inflammatory markers were normal. The Ro52 antibody was weakly positive. Electromyography showed evidence of a sensory neuropathy with myopathic features. There was symmetrical fatty infiltration and atrophy of the thigh muscles on magnetic resonance imaging (MRI). Positron emission tomography (PET-CT) scan showed widespread intense uptake in skeletal muscle groups. She was given 3 pulses of IV methyprednisolone followed by oral prednisolone which did not provide clinical benefit. Intravenous immune globulin was given when she developed bulbar weakness, with difficulty swallowing and breathing. She required non-invasive ventilation and nasogastric feed. There were necrotic and regenerative muscle fibres on the muscle biopsy, in keeping with rhabdomyolysis. Electron microscopy showed abundant lipid accumulation, suggestive of a metabolic disorder. Urinary organic acids were raised, triggering an acylcarnitines blood spot test, which were increased. This was compatible with riboflavin transport 'Brown-Vialetto-Van-Laere syndrome'. Riboflavin 500mg TDS was started resulting in significant clinical improvement. Prednisolone was weaned, genetic testing sent, and she was transferred for neurorehabilitation.

Results 

Riboflavin Transport Deficiency (Brown-Vialetto-Van Laere syndrome) is an autosomal recessive neurodegenerative genetic disorder. It affects females and males equally. Symptoms can appear in infants as well as adults. These include hearing and visual loss, bulbar palsy leading to dysphagia and speech problems. Paralysis of diaphragm may cause breathing difficulty. Initially it affects the proximal muscles and then generalized muscle weakness. Molecular genetic testing is required to confirm diagnosis. Patients may have abnormal plasma levels of flavin or acylcarnitine. Acylcarnitines are biological intermediates, used in the diagnosis of fatty acid oxidation disorders. Treatment includes riboflavin supplementation and supportive measures. Response to treatment is variable.

Conclusion 

This lady was initially managed as inflammatory myopathy but did not respond to high dose methylprednisolone. There were atypical features including normal inflammatory markers, MRI thighs showing predominantly fatty infiltration and muscle atrophy and the muscle biopsy with abundant lipid accumulation suggestive of a metabolic disorder. We are awaiting full results of genetic testing. This case is a reminder of the importance of tissue diagnosis and reassessing the initial diagnosis if the clinical picture changes or patients do not respond as expected to treatment.

Disclosure 

M. Malik: None. A. Mason: None. B. Davidson: None. J. Furby: None.