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Clinical manifestations of renal hyperparathyroidism are usually non-specific and often preceded by biochemical or imaging abnormalities.

4.3.1. Musculoskeletal symptoms

In patients with advanced renal insufficiency who have severe bone disease, bone pain is a common manifestation. This is often nonspecific in nature, and occurs in the lower back, hips, legs, and is aggravated by weight bearing (Gonzalez and Martin, 2000). Acute, localized bone pain can also become manifest and may be suggestive of acute arthritis. Pain around joints may be caused by acute peri arthritis, which is associated with periarticular deposition of calcium phosphate crystals, especially in patients who suffer from marked hyperphosphatemia (Gonzalez and Martin, 2000). The symptoms may be confused with gout or pseudo-gout.

Proximal muscle weakness is usually of gradual onset and may be severe and debilitating in some patients with advanced renal failure. Muscular weakness may be so profound that affected individuals may have difficulty getting up from a sitting position (Heptinstall, 1983). The plasma levels of muscle enzymes are normal and there are no characteristic abnormalities on electromyography (Aly et al, 1995). Proximal myopathy and muscle weakness may be related to secondary hyperparathyroidism, phosphate depletion and vitamin D deficiency. Muscle weakness may also arise as a

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result of peripheral neuropathy, electrolyte disturbances, iron overload and carnitine deficiency. Spontaneous tendon rupture has been observed in patients with long-standing renal disease in dialysis (Aly et al, 1995). The quadriceps, triceps and Achilles tendons have been most commonly implicated. Involvement of the extensor tendons of the fingers has also been described. The proximal muscle weakness is to a large extent, reversed by parathyroidectomy, which abolishes the PTH elevation. How the PTH relates to the causation of this myopathic weakness remains incompletely understood.

Spontaneous fractures most commonly affect the axial skeleton where they involve the vertebral bodies, ribs and hips. Such fractures are most commonly associated with ostomalacia (low bone turnover and poor mineralization), adynamic bone disease (low turnover pathology with normal mineralization) and/or ostitis fibrosa cystica (high bone turnover), collectively known as renal osteodystrophy (Yuen et al, 2016). Fractures often occur with minimal trauma. Thus, crush vertebral fractures may occur spontaneously, rib fractures can occur during a sneeze/cough, and hip fractures may occur such as when a patient steps off a curb. Less frequently, fractures involve the long bones (Liebross and Coburn, 1982). Spontaneous rib fractures are frequently multiple, and little displacement may be seen in chest x ray, hence, they are more easily visualized with a bone scan, indistinguishable from stress fractures or pseudo fractures (Liebross and

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Coburn, 1982). With longstanding bone resorption, patients may develop localized regions of bone loss that are often replaced by fibrous tissue, resulting in a brown tumour (Yuen et al, 2016). These brown tumours appear as well defined lytic lesions on x ray and may be mistaken for metastasis (Figure 16)

Figure 16. X ray of a 55 year old patient with renal osteodystrophy and brown tumours of the fourth metacarpal and third proximal phalanx of the left hand (arrows) (Liebross and Coburn, 1982)

4.3.2. Pruritus

This is especially common and troublesome in patients who have chronic renal failure. Substantial or total improvement may follow after parathyroidectomy. The mechanism responsible for pruritus is also not well understood, and may be related to a change in the calcium content of the skin. However, the treatment of severe pruritus is often symptomatic, but is an indication for consideration for parathyroidectomy.

4.3.3. Metastatic calcification

There are two forms of extra-skeletal or metastatic calcification (1) amorphous calcium phosphate, found in soft tissues such as heart, lung and kidney and (2) hydroxyapatite, similar to that of normally calcifying tissue present in vascular, valvular, joint and ocular tissues. Metastatic and extra-

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skeletal calcifications can occur in damaged tissue (dystrophic calcification) or in apparently normal tissue (Aly et al, 1995). This calcification occurs in a variety of tissues both visceral and non-visceral, including skin, cartilage, heart, lungs, kidneys, and shoulders, limbo-conjunctival, vascular and valvular tissues (Aly et al, 1995). Calcification of the cardiovascular tissue can affect the myocardium, atrial-ventricular conduction, and valvular function (Liebross and Coburn, 1982). This has significantly received attention as they have been linked to increased risk of cardiovascular events and death in chronic renal failure (Aly et al, 1995, Wang et al, 2003).

4.3.4. Calciphylaxis

Calciphylaxis is an unusual yet devastating syndrome characterized by skin, fat, digit and limb necrosis that is attributed to medial calcification of small and medium sized arteries. This condition has been described in patients with end stage renal failure, particularly on long term dialysis and it usually occurs in the setting of uncontrolled hyperparathyroidism. The skin lesions

initially manifest as painful nodules with peau d’orange changes which may

become mottled with violaceous discolouration similar to livedo reticularis, and can subsequently become infected. The lesions can be found in the distal extremities, involving the toes, fingers or ankles, or they may be localized in proximal areas such as thigh, buttocks, abdominal wall or breasts (Aly et al, 1995). Histologic examination of the involved skin demonstrates medial calcification of small and medium sized vessels. The pathogenesis of this

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lesion is obscure, however since these lesions are similar to those seen with warfarin induced skin necrosis, a role for altered coagulation, particularly in the protein C and S pathway in the final manifestations of this issue has been considered. Patients on dialysis with calciphylaxis have been noted to have decreased protein C and protein S activity (Kant et al, 1992). On the whole, calciphylaxis presents as a serious complication, since disseminated infection from tissue necrosis is the most common cause of death. In

general, calciphylaxis carries a very poor prognosis, even after

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