Juhani Partanen

By Juhani V. Partanen

Muscle pain is a common symptom associated with, for example, myofascial syndrome, fibromyalgia and polymyalgia rheumatica. Many diseases of the muscle tissue are, however, completely or nearly painless such as polymyositis and inclusion body myositis. Thus, a mere inflammation cannot be the cause of muscle pain. In needle electromyography (EMG), the insertion of a needle electrode causes pain but further advancement is usually painless. However, there are small spots of muscle tissue where sudden pain is elicited with the needle. In EMG, these ‘active spots’ are observed to produce spontaneous activity in the form of end plate noise and spikes (EPSs). End plate noise is elicited at the neuromuscular junction of α, β or γ motor neuron. EPSs are action potentials of γ or β motor units. Muscle spindles are the main nociceptors in muscle tissue, both in healthy muscle and in diseases with muscle pain by inflammation of the muscle spindles. Multiple possible mechanisms of muscle pain exist. Polymyalgia rheumatica may have interstitial pain and possibly pain associated with muscle spindle capsules. Delayed onset muscle soreness may reflect both interstitial muscle pain caused by minor injuries and pain generated in mildly inflamed muscle spindles.

Part of the book: Anatomy, Posture, Prevalence, Pain, Treatment and Interventions of Musculoskeletal Disorders

By Juhani Partanen, Urho Sompa and Miguel Muñoz-Ruiz

Electromyography (EMG) is routinely used in diagnostics of root syndromes in the lower extremity. By studying signs of axonal damage of different root levels in the corresponding myotomes of the lower extremity and back muscles with needle EMG reveals, which of the motor roots are injured in patients with suspected root compression. But by EMG study only injuries of the anterior motor roots are diagnosed. Routine electroneuromyography does not disclose specific injury of the afferent sensory posterior roots. However, the integrity of some the posterior roots is readily studied with myotatic reflexes. We have routinely measured a proprioceptive reflex, the H-reflex of the soleus muscle with stimulation of the posterior tibial nerve, and found it to be useful in the diagnostics of the S1 root syndrome. It seems to be possible to record H-reflex of the peroneus longus muscle at the L5 level. We discuss the serious problems with volume conduction, when trials to measure proprioceptive reflexes of the L4 and L5 levels are performed. It may also be useful to record the medium latency reflexes in the area of the posterior tibial nerve, which seems to have a different reflex arch (II-afferents – β-efferents) from H-reflex (Ia afferents – α efferents). These measurements are non-invasive and not time consuming, and we hope to be able to add them for the routine ENMG diagnostics, when appropriate.

Part of the book: Proprioception