An Aged Woman With Peculiar Legs

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HISTORY
An 81-year-old woman with Alzheimer dementia is admitted to an acute geropsychiatry hospital unit because of agitation. Medical problems include a seizure disorder, perhaps of recent onset, well-controlled on phenytoin with therapeutic levels. Grew up in Puerto Rico. Unexplained eosinophilia of 15%.

PHYSICAL EXAMINATION

Woman who appears younger than her stated age, constantly verbalizing in Spanish though not making sense even when attended by native speaker. Groans a great deal. Legs as shown. When she is not agitated, able to walk surprisingly steadily though requires contactguarding.

What's Your Diagnosis?

(Answer on Next Page)

ANSWER: RICKETS

This woman shows bowing of both legs, that is, the shins curve laterally rather than being perfectly straight. When she is clothed, the abnormality is hidden (Figure 1). If she sits, the shins look deceptively straight (Figure 2). However, when standing, a genu varum (bow-leg) deformity comes into view: the distance between the medial malleoli is much less than the distance between the knees (Figure 3).

Figure 1 – It is striking that we see no trace of leg deformities while the patient stands with the occupational therapist. Facial appearance suggests that she is part Taino, the native “Indian” people of Puerto Rico.

Figure 2 – Rachitic deformity becomes inconspicuous when she is seated. Abundant small macules of post-inflammatory hyperpigmentation lack systemic significance; minute spots of postinflammatory hypopigmentation are more widely scattered.

Figure 3 – In this view, the tibiae actually look dislocated relative to the thighs. In part as a result, knees appear oversized. They override such that their medial portions are unsupported inferiorly. One could easily mistake this contour for knee joint effusion.

We diagnosed stable longstanding deformity due to rickets. Remote vitamin D and/or sunlight deficiency was inferred. These deficiencies compromised proper architectural bone formation in a characteristic manner that would have worsened when the shins became weight-bearing.

Whether viewed from in front or behind, the knees bulge medially. The skin on the upper thighs is very extensively wrinkled. The lower thighs, calves and arms are not so wrinkled.

ONE BOWED SHIN VERSUS TWO
The bowed shin classically carries a 3-part differential diagnosis:

• Paget disease of bone usually produces unilateral deformity, often with onset in middle age or later.¹
• Rickets most commonly causes symmetrical bilateral bowing, typically first noticed between birth and age 18 months.^2-7
• Congenital syphilis constitutes an additional cause that is very rare nowadays and is more likely to produce forward rather than lateral displacement⁸; the resulting saber shins are bowed anteroposteriorly in contrast to the lateral bowing most typically seen in rickets.⁶

Much confusion arises about how rickets differs from osteomalacia. The latter is the term for vitamin D deficiency bone disease of adult onset. Because the shins are fully formed by this time, they typically do not become bowed in osteomalacia.⁷ Our adult patient with bowed shins must have acquired the deformity in childhood. While one might try to make the case that an anticonvulsant, especially phenytoin, produced osteomalacia, in fact the bone disease from this agent now is thought to be less prevalent and severe than in earlier studies in institutionalized children with epilepsy.⁹

In all forms of vitamin D bone disease-both rickets and adult osteomalacia-the histopathological defect is the opposite of osteoporosis: bone spicules have normal size and shape but are improperly calcified; whereas in pure osteoporosis they are normally calcified but undersized.

THE KNEES TAKE THE BRUNT
Although rickets can affect any bone in the body since vitamin D is so intrinsic to bone formation and healthy remodeling, those bearing weight are especially likely to suffer visible deformity. So clinically the knees are familiar sites of alteration, particularly varus and valgus deformities. Neither of these two is pathognomonic for rickets: other processes, including osteoarthrosis, can cause varus and valgus changes at the knees as well as elsewhere.¹⁰

In our patient, the head of each tibia appears subluxed- moved laterally-relative to the axis of the femur (see Figure 3). This is in addition to the tibial shaft’s seeming to tip inward (medially). The knees also look enlarged by a dependent baggy fold of flesh, most pronounced medially, with some extension anteriorly. On palpation there was no enlargement of the joint cavity, nor any redundant synovium. Nor was there an enlarged bursa, although the knee seemed to sit in a bag of water (Figure 4).

Figure 4 – This closeup emphasizes the misleading shape of the right knee, which closely mimics a joint effusion, sagging fat, or an overriding bursa distended with excess fluid.

The combination of a varus on one knee with a valgus on the other is the windswept deformity. Even a cursory glance at a person so afflicted (Figure 5) suggests how much pain accrues, and how much energy must be expended on walking.

Figure 5 – Windswept deformity in a Nigerian child with rickets is formed by genu valgum on the left and genu varum on the right. The net effect is to wreak havoc with biomechanics and stance of support. Ironically, the distance between the knees is about the same as the distance between the ankles, but no benefit accrues from this “balance of inequalities.” (Courtesy of Tom D. Thacher, MD.)

Rickets causes physical findings in many other locales, including the rachitic rosary (“rib beading”) whereby the costochondral junctions become unduly prominent and after healing are over-calcified and oversized, and distinguishable from a scorbutic rosary that reflects prior hemorrhages.11 Harrison grooves are bilaterally symmetrical transverse furrows, of controversial origin, above the level of the diaphragmatic attachment. ^2,3,7,12 Enlarged wrists are often described^6,7,13,14 but elude recognition by those who are not pediatricians. Radiographic signs are legion.

Joint involvement is described,⁷ and myopathy is part of hypovitaminosis D7; neither was identified in this case.

NEGATIVE LABORATORY TESTS
In this woman, as in about half of children even with active rickets, the serum ionized calcium and the phosphorus values were normal, perhaps because of high compensatory parathormone levels. Alkaline phosphatase was not elevated.

Serum 25-hydroxyvitamin D levels were not measured, since the patient was already receiving supplementation. At this point in her life, any progression of deformity would be attributed either to new osteomalacia, old osteoporosis with compression fractures, or the effects of abnormal force vectors over time. We thus saw the permanent structural effect of a prior vitamin deficiency, even though there was no discernible persistent or residual deficiency of that vitamin; or as Dr Kampmeier wrote half a century ago, “Such deformities after healing last throughout life.”¹⁵

While the eosinophilia made us think about cysticercosis, a cranial CT scan was negative for parasitic, vascular, or neoplastic disease. As so often happens, we wound up attributing the eosinophilia to drug effect.

The creatinine level was 0.6 mg/dL with a clearance of 68 mL per minute, as calculated using the Cockcroft- Gault equation. This finding excluded renal osteodystrophy as a cause of the skeletal changes. In renal osteodystrophy, pathologic bone lesions can result from high bone turnover, for example osteitis fibrosa cystica in secondary hyperparathyroidism; or from low boneturnover in adynamic renal osteodystrophy.^16-18

RECRUDESCENCE OF RICKETS
Nutritional rickets is a worldwide concern.19 Ordinary daily food intake in developing countries in all continents contains less than 50% of required or recommended calcium. This devastating disease has reappeared in substantial numbers in many northern countries.^20-22 Perhaps that is less surprising when one realizes that approximately 75% of girls and two-thirds of boys ages 6 through 11 have inadequate calcium intake in North America.²³

Rickets is also recrudescent in Australia-prosperous, industrialized, and sun-drenched-largely but not exclusively amongst immigrants from Africa, the Middle East, and the Indian subcontinent, including children born in Australia to such immigrants.²⁴ Rickets is common even in tropical regions: in Africa and parts of Asia, the usual substrate is not vitamin D deficiency, but dietary calcium deficiency^25,26; children with calciumdeficiency rickets often come to diagnosis in the second year of life, and as frequently via hypocalcemic seizures as from leg bowing.²⁶

It is of utmost importance to be aware of the prevalence of this reversible condition for optimal prevention of its serious complications,^24-29 and to institute corrective medical treatment early; while the orthopaedic surgeons have done wonderful operations to help those afflicted, avoiding deformity via proper nutrition makes best sense. Furthermore, prompt repletion of vitamin D and calcium can heal early rachitic changes.

INTERVENTIONS
The American Academy of Pediatrics currently recommends a vitamin D intake of at least 200 IU/d beginning in the first 2 months of life³⁰; of note, breast milk is not a good source of vitamin D, especially if the mother has limited supplies of this vitamin, so the exclusively breast-fed baby is at more, not less risk, in contrast to the situation with so many other medical problems that are effectively prevented by breast-feeding. Infants who consume 500 mL or more of vitamin D–fortified formula or milk per day need not receive the supplement. It is reasonable to administer calcium simultaneously to avoid the development of hungry bone syndrome.^2,6 Vitamin D can also be synthesized endogenously by the action of ultraviolet light on 7-dehydrocholesterol in the skin; or replaced from foods such as fish liver oils, fatty fish, cow’s milk, and breakfast cereals. The benefits of sunbaths (!) and cod liver oil were recognized and utilized in a brilliant study among at-risk infants in New Haven, Connecticut, in 1925.³¹

Dark-skinned people are at increased risk for vitamin D deficiency because melanin competes with 7-dehydrocholesterol for ultraviolet-B photons, so that vitamin D3 synthesis in the skin in response to light is diminished.

Studies have shown that vitamin D supplementation is associated with reduced risk of falls in elderly persons, improvement in muscle function, and reduced overall mortality.^32,33 In our patient, calcium and vitamin D repletion was provided to reduce the risk of subsequent osteoporosis, although we recognized that she might well already possess adequate total-body stores.

If the diagnosis is missed, a harmful intervention could be selected: adult osteomalacia can produce enough myopathy and shoulder-girdle ache to make a convincing mimic for polymyalgia rheumatica,⁷ which is sometimes diagnosed on inadequate evidence in the aged adult full of aches and pains. Normal levels of calcium, phosphate, and alkaline phosphatase are adduced as evidence against a bone disorder; if the erythrocyte sedimentation rate is a bit high, as it is in so many elders, the diagnostician is at risk of falling into a diagnostic trap. If systemic corticosteroids are prescribed, they will exacerbate the bone disease.

References:

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