Muscle Weakness and Myalgias
- A 44-year-old woman was evaluated in the rheumatology clinic of this hospital because of proximal muscle weakness and myalgias.
The patient had elevated levels of creatine kinase and lactate dehydrogenase, as well as positive tests for rheumatoid factor, anti-CCP antibodies, ANA, and anti-U1-RNP antibodies. The patient had a history of Graves' disease, hypoparathyroidism, and latent tuberculosis infection. The differential diagnosis included autoimmune diseases, overlap syndrome of rheumatoid arthritis and SLE, and overlap syndrome of rheumatoid arthritis and idiopathic inflammatory myopathy.
Diagnosis
An overlap syndrome of rheumatoid arthritis and SLE was unlikely, but an overlap syndrome of rheumatoid arthritis and idiopathic inflammatory myopathy was possible. Juvenile dermatomyositis was ruled out, and inclusion-body myositis and dermatomyositis were unlikely. The patient had a decrease in symptoms after treatment with azathioprine was started. The patient was diagnosed with hypocalcemic myopathy due to hypoparathyroidism.
Treatment
Treatment involved oral calcium citrate-cholecalciferol and calcitriol to normalize calcium levels. Thiazide diuretic agents were not used in this case to reduce urinary calcium excretion. PTH replacement therapy is not currently available but may be a promising treatment option in the future. The patient's symptoms and elevated creatine kinase level suggested hypoparathyroid myopathy as the most likely diagnosis.
Testing
Commercially available myositis panels were used to identify myositis-specific and myositis-associated antibodies. MRI and EMG were used to detect muscle injury and determine the appropriate site for a muscle biopsy. The negative MRI results decreased the probability of idiopathic inflammatory myopathies, and a muscle biopsy was not pursued. Further investigation can be pursued through electromyography, nerve-conduction studies, magnetic resonance imaging, serologic testing, or muscle biopsy.
Conclusion
Hypoparathyroidism with symptomatic hypocalcemia is the diagnosis, likely due to autoimmune mechanisms or radioactive iodine ablation for Graves' disease. Treatment includes intravenous calcium, calcium and vitamin D supplementation, and calcitriol for vitamin D replacement.