Endocrine Abstracts

Introduction: Levothyroxine is the globally preferred therapeutic compound for primary hypothyroidism. Due to expense and poor efficacy, Liothyronine is not used as first line treatment. This study was formed to answer the ESE’s recent call for data on symptomatic response to Liothyronine and predictors of that response.

Method: Patients with failure of symptomatic relief on levothyroxine were invited to try Liothyronine. 23 patients were enrolled. They underwent validated physiological and psychological evaluations which were reviewed at 3, 6 and 12 months for variation and sustainability. Weight, skin quality, mood and fatigue were taken as clinical markers of improvement. Serum thyroid factors were analyzed. Datapoints were then compared with regression analysis to identify any pre-intervention factors that could indicate treatment response.

Results: 68% reported an improvement in any clinical factor at month 3 but at month 12, only four patients had sustained improvement from baseline. This was in weight loss >2 kg (2), skin quality (1) and mood (1). Those with weight reduction also improved in at least one other category. No pre-intervention variables examined were linked to therapeutic response, neither age at onset (r=0.0004), duration of illness (r=0.04), level of Thyroid Perioxidase antibody (r=0.006), initial TSH (r=0.05), initial t4 (r=0.14) or initial t3 level (r=0.03). The sustained positive responders showed a tendency to regress towards the mean TSH value, whereas those with transient benefit suppressed.

Discussion: From meta-analyses, we expected a positive response rate varying from 15 to 30% at 1 year. Our data conforms with 17% response across all variables. The most common referral reason for ‘therapeutic failure’ was low energy and mood, yet only 8% of enrolled patients benefited. Perceived weight has been strongly correlated with symptomology and from our results, a weight loss of >2 kg at 3 months was the only objectively measurable clinical factor to indicate a successful 1 year trial. Supraphysiological dosing with liothyronine is likely the cause of the numerous but transient reported benefits at month 3 given the gradual suppression of TSH in the long term. There remains no pre-intervention indicator identified that would effectively predict response to liothyronine and thus the authors recommend that a decision to offer a therapeutic trial is left to clinician’s judgement; that they inform the patient that there is no measurable effect on mood and fatigue; that if there is not >2 kg weight loss at month 3, the medication trial should be withdrawn as there is no evidence to continue.