906 - Why Hypothyroid Myopathy Has Us Weak in the Knees

A 71-year-old female with a history of hypothyroidism on levothyroxine and liothyronine presented after being found down for four days following a ground level fall at home. She sustained traumatic rhabdomyolysis with acute kidney injury, severe dehydration, hypernatremia, and hypercalcemia. Thyroid labs from the acute hospital demonstrated normal TSH and T4 levels. During inpatient rehabilitation following treatment for rhabdomyolysis, clinical examination revealed a striking myoedema sign in the thigh. This paradox suggested an “end-organ lag” phenomenon: while pituitary feedback reflected euthyroidism, skeletal muscle tissue remained in a hypothyroid state, manifesting as delayed relaxation and localized mounding after percussion. The patient concurrently developed hypomania, which improved with low-dose aripiprazole, underscoring the neuropsychiatric variability of thyroid-related dysfunction.

Discussions:

Myoedema is a classic but underrecognized physical sign of hypothyroid myopathy, thought to result from impaired sarcoplasmic reticulum calcium reuptake and prolonged muscle contraction. Its presence in this patient despite normal thyroid indices highlights the limitations of relying solely on laboratory values to assess tissue-level thyroid function. Skeletal muscle, with its slower metabolic recovery, may remain functionally hypothyroid despite normalized circulating hormones. This patient’s underlying hypothyroid myopathy, sub-clinically treated, likely predisposed her to the fall. Furthermore, the patient’s hypomania raises the possibility of thyroid-related neuropsychiatric manifestations persisting even when standard labs appear reassuring. Together, these findings emphasize the value of bedside clinical examination in detecting occult hypothyroid effects and tailoring comprehensive care.

Conclusions:

This case illustrates that myoedema may signal persistent hypothyroid myopathy despite normal thyroid function tests, representing an end-organ lag phenomenon. Physiatrists should maintain vigilance for clinical signs beyond laboratory indices, particularly when unexplained weakness, psychiatric changes, or delayed recovery are encountered in rehabilitation patients. Recognizing myoedema can guide broader diagnostic and therapeutic considerations for functional recovery that laboratory values alone may obscure.