A 30-year-old teacher with no past medical history presented with a 3 month history of muscle weakness, pain and spasms together with cold intolerance, weight gain and fatigue. She had a baby 4 months prior to this and 2 months after delivery noticed palpitations, insomnia and tiredness which resolved spontaneously. She was a non-smoker who did not consume alcohol. She was not on any medication. There was no family history of endocrinopathy. Clinical examination revealed proximal muscle weakness with tenderness and a small non-tender goitre. There were no other positive findings. Her Creatine Kinase (CK) was elevated at 5124 U/l. Hypothyroidism was suspected but due to her clinical presentation and a raised CK; myopathy was investigated. This included a Viral screen, Cortisol, Prolactin, Vitamin B12 and D, ESR, rheumatoid factor, auto-antibody screen; all of which were normal. Primary Hypothyroidism due to Hashimotos Thyroiditis was confirmed with a TSH 190 mU/l, Free T4 <5 pmol/l and Free T3 2.7 pmol/l. Thyroid Peroxidase Antibodies >1000/U/ml. Cause for myopathy was unclear apart from Primary Hypothyroidism so she was treated with Levothyroxine which led to normalization of CK and resolution of myopathy over 4 months.
Discussion: Myofibre degeneration and decreased rate of clearance of CK from circulation has been suggested as a cause of raised CK in Hypothyroidism. Statin induced hypothyroid myopathy and myopathy due to relative hypothyroidism resulting from rapid thyroid hormone reduction in a hyperthyroid patient have been reported. This case is noteworthy in that without an apparent precipitant there was simultaneous onset of symptoms suggestive of hypothyroidism and myopathy with complete resolution of symptoms and normalization of CK with thyroxine replacement.
Conclusion: Expect recovery of myopathy to lag behind by 36 months after normalization of TSH. Thyroid function should be routinely checked in cases presenting with either myopathy or raised creatine kinase. Full case report previously published in BMJ Case Rep 2019, DOI: 10.1136/bcr-2019-230427.