Paget’s disease A progressive disorder affecting a limited number of bones. It is characterised by progressive hypertrophy and osteosclerosis of bone tissue. It leads to an abnormal increased bone turnover causing changes to bone formation. Its prevalence increases with age, and in certain countries (especially the Anglo-Saxon population), it affects up to 3 % of the population over 40 years of age. Men and women are affected equally. The aetiopathogenesis is unknown, but there has been speculation that a viral (parvovirus) infection may be implicated. The majority of osteoclasts contain intracellular particles resembling paramyxoviral nucleocapsids. Other possible causes are an inborn error of metabolism or vascular abnormalities. Paget’s disease may be inherited in an autosomal dominant trait, with the genetic abnormality localised to chromosome 18.

Paget–Schroetter syndrome – see Acute shoulder pain.

Pain It is a fundamental component of human life. Despite its aversive character, the perception of pain is a basic condition for human survival. In an acute state, it serves as a positive warning signal for the body, indicating actual or potential tissue damage. Intensive and prolonged pain, however, loses its biological significance and protective function. The pain itself becomes a source of further, often more severe damage to the body. It has a negative influence on the physical condition of the patient, disturbing his mental balance, leading to decompensation and disturbance of social communication. Persistent pain is the reason for repeated seeking of medical help and excessive use of medicaments, especially analgesics. The drop in physical activity and mental decompensation cause gradual isolation of the patient and development of abnormal, often purposeful, painful behaviour. Behavioural and psychosocial influences play an important role in the processing of pain of whatever origin; however, their importance rises with chronicity. Chronic pain is therefore considered a complex biopsychosocial phenomenon.

Painful arc Shoulder pain elicited on abduction of the arm between 60 and 120°. Pain occurring in this range is typical of supraspinatus tendon or subacromial bursa involvement. Pain at the end of the arc between 160 and 180° indicates an affection of the acromioclavicular joint.

Panniculitis Inflammation of subcutaneous fatty tissue manifested by the formation of inflamed nodules, particularly in the lower extremities, thorax and gluteal area. It mainly affects women in early and middle age. Many forms of panniculitis with or without vasculitis are described, including acute lobular panniculitis without vasculitis (Weber–Christian disease) and panniculitis associated with a connective tissue disease, pancreatic disease (pancreatitis or pancreatic carcinoma) or lymphoma. It consists of a heterogeneous group of symptoms, in which inflammation in fatty tissue occurs, particularly in subcutaneous fatty tissue. The histopathologic picture shows infiltration of neutrophils or lymphocytes, later followed by histiocytic infiltration and possibly large cell infiltration. Lesions settle by fibrosis formation. In the phase of histiocytic infiltration, panniculitis can have the property of granulomatous inflammation. Subcutaneous fatty tissue has a lobular structure. Central arteries pass through the fatty lobules forming branches of arterioles and capillaries, from which the blood is conducted through venules located in septa between particular lobules. Panniculitis affecting venules in the septum between lobules can be schematically classified as septal (non-necrotising) panniculitis and lobular (necrotising) panniculitis, which affects the artery passing through the centre of the lobule.

Panniculosis A noninflammatory disease of subcutaneous tissue incorrectly known as cellulitis. It is a constitutional disorder of fatty tissue deposit predominantly occurring in women during menopause.

Pannus Proliferating synovial tissue with activated fibroblasts and inflammatory cells infiltration (lymphocytes, plasma cells, activated macrophages and dendritic cells) which intensively grows into the surrounding bone on the joint margin causing local osteolysis. The typical picture of bone erosion therefore develops. A frequent finding of multinucleated cells with phenotypic characteristics of osteoclasts in the interface between bone and pannus led to the presumption of direct involvement of the cells derived from the pannus in bone resorption. The focal inflammation in rheumatoid arthritis affects subchondral and juxta-articular bone, where pannus development begins.

Paracetamol One of the most frequently used non-opioid analgesics. Missing an anti-inflammatory effect, it cannot be included in the group of non-steroidal drugs (NSAIDs), even though recently published trials suggest that paracetamol, particularly in the central nervous system, inhibits the COX-3 isoenzyme. It does not affect the production of physiologically important prostaglandins in the stomach, bowel or platelets, and therefore there are none of the typical adverse effects observed when using NSAIDs such as increased risk of gastrointestinal bleeding or an acute decrease in renal function. A daily dose higher than 5 g/day may cause fatal liver impairment. The analgesic and antipyretic effect is comparable to that of aspirin. Paracetamol has neither an anti-inflammatory nor anti-aggregate effect. The analgesic properties of paracetamol will last for around 4 h due its short half-life of about 2 h. Administration of higher doses (more than 2 g a day) may cause prolongation of the prothrombin time. Compared to aspirin, paracetamol has a lower ceiling effect. It can pass through the blood–brain barrier, and only a small amount is bound to plasma proteins (approximately 10 %). It is metabolised in the liver and is eliminated via the kidneys in the form of glucuronides and sulphates.

Paraesthesia Decreased or tingling sensation of the skin in particular dermatome.

Paraffin wax A mixture with approximately 5 % of paraffin oil, heated to 55–60 °C, is used for therapeutic purposes. The heat that is released during transformation from a liquid to a solid state is utilised. The manner of use includes soaking the limbs in paraffin wax and transferring the paraffin wax using a paintbrush or suitable tissue soaked several times in the paraffin wax and, most favourably, using plastics. It is necessary to keep the skin dry in the area of paraffin wax administration as different tolerability of the skin to paraffin wax (60 °C) and water (46 °C) may cause burns. The mixture of paraffin with peloid sheets, so-called parafango, is also frequently used. They are indicated for chronic pain of the musculoskeletal system, noninflammatory arthrosis, extra-articular rheumatism, vertebrogenic pain syndrome, spondyloarthropathies and rarely also for inactive ankylosing spondylitis as a form of preheating before exercise.

Paraproteins Monoclonal immunoglobulins present in the plasma of patients with multiple myeloma or Waldenström’s macroglobulinaemia (gammopathy), monoclonal gammopathy of undetermined significance, cryoglobulinaemia, plasmacytoma, amyloidosis, heavy chain disease, lymphomas, leukaemias and some other diseases.

Parathormone The most important regulator of extracellular calcium but also has a direct effect on bone. It influences the hydroxylation of vitamin D and reabsorption of calcium in the kidneys. The effect of PTH on bowels is indirect via calcitriol (increase of calcium resorption from the bowel).

Parathormone drug – Teriparatide The only pure osteoanabolic drug indicated for the treatment of severe postmenopausal osteoporosis (previous fracture and T score <2.5 on BMD scan). A synthetic recombinant aminoterminal fragment (1–34) of parathormone is used. When used in a therapeutic dose of 20 μg/day subcutaneously, it does not produce osteoporosis as occurs in hyperparathyroidism, but instead the osteoblastic production of growth factors IGF-I and TGF-beta increases, without reducing the production of osteoprotegerin. Teriparatide reduces the risk of vertebral and non-vertebral fractures and greatly increases BMD in the most at-risk groups of patients. Treatment significantly improves pain and quality of life. It is administrated for 18–24 months.

Parathormone-related protein (PTHrP) The most frequent cause of hypercalcemia in malignancies without bone metastases is the secretion of parathormone-related protein. This protein is produced by squamous cell carcinoma; by carcinoma of the kidney, breast and urinary bladder and ovarian cancer; and also by some non-Hodgkin lymphomas and in chronic myeloid leukaemia. It is also called humoral hypercalcaemia of malignancies. Secretion of endogenous parathormone is suppressed in these cases. Since the PTHrP molecule is partially homologous, through binding to the same receptor, it simulates the parathormone effect and therefore increases bone resorption and tubular re-absorption of calcium in the kidneys. The diagnosis of humoral hypercalcemia may be confirmed by high serum concentration of PTHrP.

Paroxysmal nocturnal haemoglobinuria A rare form of haemolytic anaemia with intravascular haemolysis during sleep due to a greater sensitivity of the erythrocytes to haemolysis by an autologous complement. As well as affecting erythrocytes, neutrophils and thrombocytes also have a higher sensitivity to the haemolysis. The cytoplasmic membranes of these cells are deficient in DAF, the decay-accelerating factor that protects against damage after spontaneous activation of the complement. The disorder is characterised by leucocytopenia, thrombocytopenia and iron deficiency and often by the presence of blood (haemoglobin) in the urine.

Parvovirus arthritis Parvovirus B19 was associated with clinical disease in the early 1980s. In children, it produces slapped cheeks disease (fifth disease, erythema infectiosum) but in female adults, it can produce an acute arthralgia/arthritis mimicking rheumatoid arthritis. Symptoms usually settle within 3 weeks, though occasionally last up to 6 months. The diagnosis can be confirmed by IgM antibodies to parvovirus within the serum. Only symptomatic treatment and reassurance are required, though rarely it can produce a transient aplastic anaemia and miscarriage in pregnancy.

Pathergy phenomenon Scratching the skin using a sterile needle evokes a strong erythematous reaction with induration. The test is positive in active Behcet’s disease as a sign of skin impairment (vasculitis). It is present more frequently in the Turkish population than in Europeans and Americans.

Pauciarticular juvenile idiopathic arthritis – see Juvenile idiopathic arthritis (JIA).

PCR (polymerase chain reaction) A laboratory technique that makes it possible in an automated way to gain millions of copies of a fragment of a DNA molecule by in vitro enzymatic replication. The segment of double-chain DNA isolated from, for example, lymphocytes and containing the required gene is marked by complementary oligonucleotides (primers). The segment undergoes amplification by repeated cycles of denaturation, cooling and primer attachments and their subsequent prolongation using thermostable DNA polymerase. One cycle takes approximately 3 min and results in duplication of a DNA fragment. This means that within 60 min, more than two million copies of one DNA fragment can be produced. PCR can be used in medical and biological research for prenatal and common diagnostics of genetic, infectious and other diseases, in determining their pathogenesis, in the genetic determination of individual and populations and in resolving the most fundamental problems of contemporary molecular biology and medicine.

Peak bone mass (PBM) PBM is the maximum bone mass usually achieved in the third decade of life. The level of achieved peak (maximum) bone mass is influenced by genetic, hormonal, nutritional factors, physical activity, muscle mass volume, chronic diseases (especially inflammatory) and medications (glucocorticoids).

PEG Abbreviation for polyethylene glycol; a synthetic molecule with variable relative molecular weight. It is used for precipitation of soluble proteins including circulating immune complexes and as a fusogen in hybridoma technology of monoclonal antibodies production.