The purpose of this study is to investigate the presence of central sensitization in vitamin D deficiency and its effect on cutaneous silent period, pain, and quality of life. The secondary purpose of the study is to investigate whether a change in cutaneous silent period parameters, pain severity and neuropathic sensitization and quality of life after vitamin D replacement.

Vitamin D deficiency is a pandemia. Main causes of this is insufficient exposure to sunlight. Vitamin D deficiency is related to conditions like various cancers, autoimmune diseases, hypertension and growth retardation in children (1).

International Association for the study of pain has defined pain as "An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." (2). Pain lasting longer than 3 months has been deemed as chronic pain (3). Vitamin D deficiency influences various types of pain, including chronic pain (4,5,6,7).

Vitamin D influences the musculoskeletal system via the calcium-phosphorus metabolism and the receptors found in skeletal muscle cells (8). Vitamin D deficiency has been shown to decrease muscle strength, the this decrease in proximal muscles affect postural stability and can increase falls. Vitamin D deficiency also causes problems in bone mineralization, causing isolated or widespread pain in muscles, bones and joints. These patients end up getting wrong diagnoses such as fibromyalgia, osteoarthritis, inflammatory arthritis, and chronic fatigue syndrome (1,7). Vitamin D deficiency causes hyperinnervation and hypersensitivity on nerves and cause pain to be felt more intensely (5).

In a normal skeletal muscle, during an isometric contraction, a number of motor unit will be activated. These motor units produce a stable electromyography pattern and keep their own frequencies during contraction. If the nerve, tendon or a cutaneous nerve nearby is stimulated, electromyographic activity is disrupted and a bioelectric silence occurs. This is called cutaneous silent period (CSP). It is an inhibitory spinal reflex and its afferents consist of A-delta nerve fibers.

In various studies, CSP has been shown to be clinically beneficial in conditions like peripheral neuropathy, syringomyelia, Parkinson's disease, restless leg syndrome and fibromyalgia.

von Känel R et al. has investigated the effect of vitamin D deficiency on widespread pain index (WPI) and symptom severity score (SSS) and found out that it increases central sensitivity (8). In thei study, thy did not utilize any electrophysiologic objective measurements. Akyüz et al. have investigated the effect of vitamin D deficiency on chronic pain and nerve conduction studies; they have shown that vitamin D is correlated with various nerve conduction parameters while these parameters do not change after replacement (9,10).

Patients with vitamin D deficiency and healthy controls with normal vitamin D levels will be compared in terms of cutaneous silent period parameters, pain severity and neuropathic sensitization and quality of life. Cutaneous silent period parameters (duration and latency ), The Leeds Assessment of Neuropathic Symptoms & Signs and Nottingham Health Profile will be used for the assessments. Patients with vitamin D deficiency will receive vitamin D supplementation therapy. Before and after therapy, cutaneous silent period parameters, LANSS scores and Nottingham Health Profile will measured before and 8 weeks after starting vitamin D supplementation therapy.

Inclusion Criteria

• Presence of widespread pain
• Presence of vitamin D deficit

Exclusion Criteria:

• Any contraindication of performing silent cutaneous period
• Any contraindication for vitamin d use
• Presence of conditions that affect cutaneous silent period like the presence of carpal tunnel syndrome and polyneuropathies
• Defective peripheric autonomic nervous system findings
• Not being able to write and read
• Not being able to communicate