Clinical features:
(1) hypothyroidism (although this may be unsuspected)
(2) muscle weakness, often involving proximal muscle groups
(3) muscle stiffness
(4) muscle cramps
(5) muscle pain (myalgia)
(6) slow relaxation of deep tendon reflexes
(7) variable dysarthria with slurring
(8) improvement with thyroxine replacement
Muscle cramps may be worse after exercise or in cold weather.
Laboratory findings:
(1) low serum thyroxine concentration and elevated serum TSH
(2) elevated serum myoglobin concentration
(3) elevated serum creatine kinase (CK) concentration
Electromyography (EMG):
(1) myopathic pattern
(2) variable fibrillations or other form of spontaneous activity
Specific syndromes of hypothyroid myopathy::
(1) Hoffmann’s syndrome
(2) Kocher-Debre-Semelaigne syndrome
