I used to have widespread muscle/joint pain from the 4th month on levothyroxine.. Couldn't bend knees, raise arms etc, body wouldn't bend so I couldn't get into a car etc.etc.
I don't anymore they all disappeared with adequate thyroid hormone. This is an extract from Dr Lowe who dealt with thyroid hormone deficiency, fibroymyalgia and another website Thyroidscience:-
However, I personally don't believe that measuring the free T4, free T3, or any other circulating hormone level, is the most effective clinical approach. My belief is based partly on the the studies of Escobar-Morreale and colleagues in Spain. Their study results make one thing clear: Circulating free T3 and T4 levels don't allow us to accurately predict the T3 concentration in the cells of most tissues. The evidence suggests that there is simply too much variability between different tissues in the same patient. Moreover, there's too much variability between the tissues of different patients. Even more difficult is accurately predicting the physiological and clinical effects of different circulating free T3 and T4 levels. Again, there's simply too much variability to allow accurate predictions.
Barnes was right when, long ago, he wrote that circulating levels of hormones don't measure what's most important—how the patient's tissues are responding to a dosage of thyroid hormone. Our regimen involves multiple measures of how tissues are responding to a particular dosage, repeated at short intervals in a highly systematic way. Our model of assessment is taken from behavior modification, in which I was trained in the early 1970s. We know from hundreds of trial runs that we can precisely control the metabolic status of most patients only by using these multiple measures of tissue response. We adjust each patient's dosage until these measures tell use we've achieved normal tissue metabolic status—regardless of what the patient's circulating hormone levels are. I concede that you can do some fairly good tweaking by using free T3 and T4 levels. But still, if the patient's tissue responses aren't carefully assessed, the clinician isn't focusing on what's most important—the patient's physiological and clinical responses to treatment.
For the moment, let's accept this qualification for the sake of illustration and rephrase your question: Is there a thyroid gland problem that could result in a normal T4 level and a low T3 level? Theoretically, the thyroid gland may dysfunction in such a way that it secretes normal amounts of T4 but less-than-normal amounts of T3. This could result in a normal circulating T4 level and a low T3 level. T3 is the most metabolically active thyroid hormone, but a low circulating T3 level may not result in slowed metabolism and related symptoms. The reason is that most T3 inside cells, where the hormone drives metabolism, is derived from the conversion of T4 to T3. As long as enough T4 reaches the cells and the cells convert enough T4 to T3, metabolism may be normal despite the low circulating T3 level.