Abstract
SLONM is an exceedingly rare disease, with often long delays in diagnosis and severe functional disability. Approximately half of patients have an associated monoclonal gammopathy of unknown significance (MGUS). Immunotherapy can be restorative for some patients but often requires second or third line therapies.
A 68 years old lady presented with a 6 month history of progressive hip girdle pain, altered gait and difficulty climbing stairs. On examination she had a lower limb isolated proximal myopathy. She had no toxic exposures nor relevant family history. Her extensive blood work up was remarkable only for a low-level IgG lambda paraprotein of 3g/l in keeping with MGUS.
Her neurophysiology demonstrated myopathic changes of the iliopsoas and quadriceps. Her MRI demonstrated oedema with some fatty atrophy of hip girdles bilaterally. The muscle biopsy of left iliopsoas demonstrated non-specific changes of denervation, myopathy and a small degree of inflammatory infiltrate. She underwent Facio-Scapulo-Humeral-Dystrophy (FSHD) testing which revealed a false positive due to genetic rearrangement which delayed diagnosis. A muscular panel was non-contributory. She trialled immunoglobulin, corticosteroids and mycophenolate without benefit.
She continued to clinically deteriorate and at the 24 month mark now had head drop, camptocormia, bulbar and upper limb weakness. She underwent repeat muscle biopsy which revealed myopathic changes with nemaline bodies suggestive of SLONM. She is currently undergoing escalation in immunotherapy after myeloma was diagnosed on bone marrow aspirate.
This case highlights the challenges in making a diagnosis of SLONM, the need for repeat investigations, associated hematological conditions and immunotherapy considerations.
